[Feature] Updated page header. Added new authoring edit form.

Details:
1. added header icons;
2. changed img to background-image in header;
3. replaced old authoring header buttons with new UI form
[Feature] Added navigation, refined show/close methods
[Feature] Fixed CSS and visual appearence.
[Feature] Implemented canvas edit button for timelines, exhibits and content items.

Details:
1. added svg support for web-service;
2. placed edit authoring buttions inside authoring form;
3. added clickable svg images (edit buttons) for timeline (bottom right corner), exhibit (between exhibit title and exhibit top border), content item (bottom right corner).