Organize toolbars and other map actions in a sidebar

[dkastl]

Problem
The current toolbar and icons used are inconsistent, in particular the layer switcher button.
Additionally it's difficult to add more content-rich controls,for example GeoJSON upload field.

Improvement
The sidebar allows to organize toolbars and map related content different, more consistent. It has less space restrictions, allows to add additional information to help users. As the GTT map is rather wide than high a sidebar also fits well without taking lot of usable space.

More information:

• https://github.com/Turbo87/sidebar-v2
• https://turbo87.github.io/sidebar-v2/examples/ol3.html
• https://codepen.io/viglino/pen/vxGOQN

The following sidebar tabs would replace the current icons

• Editing (incl. GeoJSON upload)
• Search
• Layers

New tabs could be

• Help
• Settings

Zoom buttons as well as Location and Maximize icon could remain buttons.

This is issue is related to #102 and #101

[dkastl]

The sidebar library doesn't seem to be well maintained, and the current Improved buttons are fine IMO