splash-screen: Add ability to redirect to a splash screen URL

Checks for the presence of a cookie with specific values when activated,
and redirect the user to a configurable URL when it is not found, or not
with an accepted value.

To be used to display a splash screen to users upon the first visit.
It's the responsability of the splash page at the redirected URL to set
the proper cookie value before sending users back to the LMS.
Update Esperanto (dummy) translation files
Merge pull request #2403 from edx/dcadams/tinymce_mods

Addition of 3 TinyMCE plugins to toolbar
Merge pull request #2564 from edx/sarina/new-esperanto

Update Esperanto (dummy) translation files
i18n points possible display LMS-2201
Update i18n translator documentation
Merge pull request #2568 from edx/sarina/update-i18n-translator-docs

Update i18n translator documentation
Merge pull request #2531 from edx/sarina/LMS-2201

i18n points possible display LMS-2201
Merge pull request #2482 from edx-solutions/splash-screen

splash-screen: Add ability to redirect to a splash screen URL
first commit to the branch

Added fix to horizontal extension in the TinyMCE RichText-Annotator.

Also includes trying to add annotator to Studio. Only thing failing
currently is getting TinyMCE to work at all.

Adding fixed to merging conflicts

Added folksonomic tags for annotations and also added the ability for video annotation to work on studio minus tinymce

Adding License to Tags plugin