Bug 991509 - Adding Tamil input method for B2G

Cherry-picked from 5a8f0e4f9e146dc2fdd2317841819ea5aa9f5211

Conflicts:

	apps/keyboard/style/keyboard.css
	build/config/keyboard-layouts.json
Merge pull request #23122 from luke-chang/991509_v1.4_tamil_input_method

Bug 991509 - Adding Tamil input method for B2G