Actually register the SSA subtitle format
Add Ukrainian translation. Closes #1809.
Update boost to 1.56

Closes #1818.
Update wx

Removes the need for the RTL hacks in BaseGrid as the bugs have been
fixed properly in wx.
Handle json parsing errors when loading shift times history

Closes #1802.
Perform extradata deduplication on add.

Checks all existing extradata keys and values to ensure that the set
that is being added doesn't already exist.
fix permissions in INSTALL_FLAGS
Fix loading subtitles extradata from matroska files
Optimize Extradata handling a bit