Update CREDITS

Added it translator
Update locale dialog.
Make all local Cocoa variables non-const.
Disable native clipboard glue classes with Qt 5.
FIXED: Crash when ignoring words in spelling dialog.

This commit reverts 9d1f39576c5c1bc29235817cf8dc6fa2fe977651.
Simplify build system file.
Update copyright year.
Sync translations with Transifex.