* Convert to "container-based" travis build

Since all ppa sources used are currently whitelisted by Travis, why don't we convert to a "sudo-less" structure that promises a shorter build start time?

* Explicitly disable sudo in Travis

* Fix #2108 - Fix gif uploads
Add specs for media attachment gifv conversion

* Add ffmpeg to travis

* Make travis install ffmpeg, not libav

* Switch travis to trusty

* Rename admin.domain_block to admin.domain_blocks in prep for i18n improvement

* Use implicit controller/action path for i18n in admin/domain_blocks

* Add DomainBlock#accounts has_many

* Avoid i18n health warning for `en` locale by using symbol scope with :count

* Remove unused i18n key: plaintext_secret_html

* Remove unused i18n key two_factor_auth.warning

* Remove final will_paginate i18n keys

* Remove unused key two_factor_auth.recovery_codes

* Remove unused key: admin.reports.comment.none

* Remove unused reports. i18n namespace (moved to admin.reports)

* Ignore keys from locales which override activemodel and activerecord errors

* Revert "Remove unused key: admin.reports.comment.none"

This reverts commit 350ef2685f.

* Update i18n key reference to match moved location

* Add missing `en` keys to i18n

* Tell i18n-tasks to ignore missing attributes that dont need overwriting

* Add i18n-tasks unused to travis

The 4.x branch [entered maintenance](https://github.com/nodejs/LTS#lts-schedule1) on 1 April.

* Update rspec-rails to version 3.5.2

* Update addressable to version 2.5.1

* Update autoprefixer-rails to version 6.7.7.1

* Update bullet to version 5.5.1

* Update domain_name to version 0.5.20170404

* Update letter_opener_web to version 1.3.1

* Upate redis-rails to version 5.0.2

* Update active_record_query_trace to version 1.5.4

* Update capistrano-rails to version 1.2.3

* Update dotenv-rails to version 2.2.0

* Update pg to version 0.20.0

* Update tilt to version 2.0.7

* Update warden to version 1.2.7

* Update tins to version 1.13.2

* Update terminal-table to version 1.7.3

* Update oj to version 2.18.5

* Update simplecov to version 0.14.1

* Update uglifier to version 3.1.13

* Update hashdiff to version 0.3.2

* Update webmock to version 2.3.2

* Update devise to version 4.2.1

* Use ruby version 2.4.1

* Update sass to version 3.4.23

* Update puma to version 3.8.2

* Update will_paginate to version 3.1.5

* Update font-awesome-rails to version 4.7.0.1

* Update fuubar to version 2.2.0

* Update pry-rails to version 0.3.6

* Update simple-navigation to version 4.0.5

* Update rubocop to version 0.48.1

* Update doorkeeper to version 4.2.5

* Update faker to version 1.7.3

* Update aws-sdk to version 2.9.5

* Update fabrication to version 2.16.1

* Update hamlit-rails to version 0.2.0

* Update http to version 2.2.1

* Update httplog to version 0.99.2

* Update sidekiq to version 4.2.10

* Update rspec-sidekiq to version 3.0.0

* Update pghero to version 1.6.4

* Update rack-cors to version 0.4.1

* Update i18n-tasks to version 0.9.13

* Update ruby-oembed to version 0.12.0

* Update jquery-rails to version 4.3.1

* Update simple_form to version 3.4.0

* Update react-rails to version 1.11.0

* Update aws-sdk to version 2.9.6

* Update sidekiq-unique-jobs to version 5.0.0

* Update uglifier to version 3.2.0

Try to fix Travis CI setup

fix tests (the recorded Salmon fixture expects LOCAL_DOMAIN to be something
specific unfortunately)

when registering incoming status mentions, add Travis CI file