Updated some string translation functions in i18ncontent
Fixed minor issues with i18n and settings forms

- Fixed: Translated primary and secondary links appear even if they are disabled, by yrocq #631388

- Added: Primary and secondary links' menus translation using preprocess, by neochief, #514108

- Fixed: Checkboxes fields are not translating in profile view pages, by neochief, #520692

- Fixed i18n Filter in Views results in SQL Error, by markus_petrux, #522162

- Cleaning some module dependencies and old code.

- Added: Translated taxonomy tokens by Hugo Wetterberg, googletorp, #344794
- Fixed: Global variable corruption by etzel, #580280

* Use db_add_field() for update_6000.

"uk-ua" is absolete tag for Ukrainian translations, "uk" is correct, so removing useless translations.

- Fixed: Unset variables set to be multilingual don't show default values, by Island Usurper, #527534

- Added node language options:
  - Default to current language
  - No language neutral
  - Lock language once created