Add missing dependencies

Removed
* github.com/gogits/cache
* github.com/gogits/session

Slack Support

Update german translation with PR #404

Update locale_de-DE.ini

Add missing 'new migration' link

Addresses issue #399

Conflicts:
	dockerfiles/README.md

Update locale_zh-CN.ini

Update locale_en-US.ini

Update locale_de-DE.ini

Double entry of "config.log_config"

Double entry of "config.log_config"

Removed trailing white spaces

Removed trailing whitespaces with

```sh
for file in `grep -r " $" * | cut -d : -f 1 | sort | uniq | grep -v " "`; do sed -i 's/[ \t]*$//' $file; done
```

and some handwork.

Update locale_en-US.ini

Update locale_de-DE.ini

Update locale_de-DE.ini

Add missing translation keys and add some german translations

Update locale_de-DE.ini

Add missing translation of "locale_en-US.ini"

Migrate all branches and tags

Remove newline characters from ssh key before processing it.

Fixes issue #370: https://github.com/gogits/gogs/issues/370