[Azoth OTRoid] Fixed OTRv3 support.

Added limited support of instance tags. Previous temporary solution is not
needed anymore. (Affects only build with libotr 4.x.)
Merge pull request #304 from tehnick/fix-otrv3-support

[Azoth OTRoid] Fixed OTRv3 support.
[Core] Added clear line edit addon to plugin filter.

Closes #1475.
[Azoth Rosenthal] Updated translations.
[Azoth OTRoid] Fixed otrv3 build.