Translations: Switch to Transifex format

- Based on new (last) translation download from getlocalization.com
- Removed untranslated strings. Getlocalization started including those at some point
which is highly annoying, unnecessary and breaks the new transfix system,
since it'll mark all of the english strings as actual translations
- Avoid dots in entities. It confuses the Transifex YML parser
- Removed some locales unknown to Transifex which didn't have any translations anyway
- Removed "lolcat" locale, uses custom notation (en@lolcal)
  which SilverStripe's i18n system can't handle
  (needs mapping from SS naming to Zend naming)
- Renamed "Te Reo/Maori" locale from "mi_NZ" to "mi" (Transifex/CLDR notation)
- Namespaced all entities used in templates (deprecated usage)
- Converted dots to underscores where template filenames are used for namespaces,
since Transifex YML parsing handles them as separate YML keys otherwise
- Removed whitespace in entity names, SilverStripe i18n can't handle it
- Only allow selection of locales registered through i18n::$all_locales to avoid
  issues with unknown locales in Zend's CLDR database
Merge pull request #2291 from chillu/pulls/transifex-3.0

Translations: Switch to Transifex format (3.0)
Update en.yml

Added missing string Security.LOSTPASSWORDHEADER
Merge pull request #2304 from wernerkrauss/pull/translationstring-security

Update en.yml
Fixed "session started" error on install.php
Create folder if required in dev/generatesecuretoken
Merge remote-tracking branch 'origin/3.0' into 3.1

Conflicts:
	admin/templates/Includes/LeftAndMain_Menu.ss
	admin/templates/Includes/ModelAdmin_ImportSpec.ss
	admin/templates/Includes/ModelAdmin_Tools.ss
	admin/templates/LeftAndMain.ss
	admin/templates/ModelSidebar.ss
	i18n/i18n.php
	templates/ComplexTableField.ss
	templates/ComplexTableField_popup.ss
	templates/FileIFrameField_iframe.ss
	templates/Includes/GridFieldItemEditView.ss
	templates/Includes/TableListField_PageControls.ss
	templates/RelationComplexTableField.ss
	templates/TableField.ss
	templates/TableListField.ss
Fixed merge error

See 00ffe72944e004e1dbbbad43fe644b733053d4a9