Merge pull request #13977 from alefteris/bug-942580-kb-final-sigma

Bug 942580 - Remove duplicate "final sigma" from Greek keyboard.
r=rudylu(cherry picked from commit 6b4dd7baa58fbba70161d7979d8503f8fb9f64df)
a=timdream
Merge pull request #13975 from alefteris/bug-942575-kb-greek-l10n

Bug 942575 - Translate Greek keyboard menu labels.
r=rudylu(cherry picked from commit 0904f366263eca59f61afb9c340004f91e488870)
a=timdream