Allow icons to be framed

Since icons are images too it should be possible to use them with the `.framed` class.
Support multipart/form-data in HTTPRequest

Closes #1457
Merge pull request #1410 from max-m/patch-4

Allow icons to be framed
Added support for application-specific classes during installation
Merge branch 'master' of github.com:WoltLab/WCF
Small optimization
Merge branch 'master' of github.com:WoltLab/WCF
Added favicon within ACP
Merge branch 'master' of github.com:WoltLab/WCF
Fixes versionable database objects
fix travis error
Fix MySQLDatabaseEditor
Fix uninstallation of plugins with versionable database object
Fixed resize of cached images
Updating minified JavaScript files
Fixed import issue
Fixed import of embedded attachments
Merge branch 'master' of github.com:WoltLab/WCF
Merge branch 'master' of github.com:WoltLab/WCF
Fixed spoiler bbcode