Refactor lobby terms and conditions UI from rP21847 / D1568 to a new terms dialog UI and reuse that for mod.io and the UserReporter, refs #5257, #5218.
Reuse all existing strings, use a FileExists hack for mod.io until the new strings are committed.
Rename prelobby/common/terms/terms.js to termslobby.js for easier distinction from common/terms.js.
Based on patch by: bb
Differential Revision: https://code.wildfiregames.com/D1602
refs https://code.wildfiregames.com/D1601
refs https://github.com/bb-bb/0ad/tree/terms
refs https://github.com/elexis1/0ad/tree/terms