l10n_client 6.x-1.5

Changes since the 6.x-1.4 version:

• #320512 suggestion by hadi farnoud: The strings list should be RTL.
• #287210 by Jose A Reyero: features ported forward from the 5.x version (slightly modified)
• #291156 reported by multiple people, patch by myself: drop any strings found before our hook_init() is called. Other modules could invoke t() in hook_init() before our code runs, and that loads in the whole locale cache, which could hang browsers if fed into the l10n_client UI.
• #313796 by hass: cleanup only selected text groups; also adds support for reimporting multiple languages at once