Files: Selection options

[szaimen]

Please add these ribbon options for selection:

• [x] Select all
• [x] Select none
• [x] Invert selection

Would be really helpful especially for touch input.

This is how it is currently implemented in the file explorer:

[yaichenbaum]

Select all and clear all are already options. Since the idea is straightforward I will go ahead and approve this issue.

[szaimen]

I just don't know, if these option are fitting well in the "Layout" category. But that is a discussion for another time.

[yaichenbaum]

Selection options are fully implemented with v0.7.6.