Refactor modal dialogs throughout the app

• remove dialogs from *.page.js components and handle them in the ui components (from Question.page -> Question, ExportToWordButton, ExportToScormButton and from ManageUsers.page -> UserList)
• remove box-shadow from Buttons
• add custom footer for all dialogs, so that we can pass our own Button to them
• increase Link component's style specificity so that it displays correctly inside dialogs
• add colorInfo variable to the theme, same as colorPrimary

Testing notes: please check all instances of dialogs throughout the app and make sure they work fine and are properly themed:

• dialogs in Question page when submitting, moving through review steps and create new version
• dialogs in Questions found in Discover (so published questions) when clicking "Previous question" when item is first on the list and "Next question" when item is last in the list
• dialogs when exporting to word
• dialogs in User management page before deactivating, deleting or activating
• terms and conditions in Signup page