Fix word-break in account profiles

Add link to instances.mastodon.xyz

It's just an upstream merge

word-break:break-all is a surefire way to break things. It should be set
to normal.
This merge just set it back to what it should be.
Tested on Firefox 52.0.2 and Chrome 56.0.2924.87 with no detected
errors.

admin UI

Adding social.mashek.net

Updated list of instances for gay.crime.team

Add IPv6 column in list and remove dead instance

This is done after some complaints I saw on Twitter about the lack of IPv6 support on Mastodon instances.
Also, seeing this may encourage instances owner to add IPv6 support to their own.

Updated out-of-date info for gay.crime.team

improve video button visibililty (issue #713)

Add social.targaryen.house to instances list

Add mastodon.xyz to instances list

Put line breaks between API methods in docs

Clarify post privacy warning

Mastodon is not an alternative, it is a solution

This month I traveled to Cambridge, Massachusetts with my friends and attended LibrePlanet 2017. At the talk *Technology for direct actions*, Andrew Seeder pointed out that we often call free software an "alternative" to what exists. But an alternative is something that is mostly similar, and differentiated by preference rather than need. For instance, a trackball is an alternative to a mouse, but a jail is not an alternative to a bedroom. Andrew suggested that we start looking at free software as "solutions" rather than alternatives. So I propose boldly proclaiming that Mastodon is not an alternative to Twitter, but rather a solution to it.

Needs to be a separate task with no locking