Invert selection for student table

[hisahi]

Short description

Adds a button to invert selection

DoD

I have:

• [x] added actual code.
• [x] produced clean code that passes ESLint.
• [x] code that actually does what it should.
• [ ] documented the code or added documentation to the wiki.
• [x] added or modified test(s).
• [x] test(s) that actually pass.

[Mamelukki]

Are the invert and select all buttons too close to each other? Otherwise looks good.

[hisahi]

It's possible to increase the margin if necessary