[Feature] Fixed few bugs with authoring. Fixed bug #306. Some code review fixed;

Details:
1. Fixed bug #306 - Dates in Cosmos Exhibits are displayed negative using long form;
2. fixed alert window when timeline was removed;
3. fixed exhibit's date in edit exhibit form (it was exhibit.date - exhibit.width / 2, now it's exhibit.date);
4. removed obsolete mouse handlers in authoring.ts for edit modes;
5. removed some obsolete code from authoring.ui.ts;
6. fixed few bugs with active icons in header;
7. capitalized regimes links