Targeted string customization in the lms UI

Add the text_customization dict in advanced settings, which contains
customizations checked in specific spots. Here it is used to enable
the customization of the "Check" and "Final Check" button titles.
In progress review
Shuffle feature for multiple choice questions
Revert not supposed to be in this branch

This reverts commit 854bb7d6ec91c52c42233ef6a0ec6c5e8db3c74d.
Revert not supposed to be in this branch

This reverts commit 3507cebc52365089aaebb960da7577064b874bd2.