Add class for components

[LuomaJuha]

Adds a class for components, so adjusting styles locally is easier. Small adjustments to the code.

[demiankatz]

Thanks, @LuomaJuha -- see below for a few questions, comments and suggestions.

[demiankatz]

Thanks for addressing all of my comments, @LuomaJuha -- just a couple more thoughts now...

[EreMaijala]

Now that I gave this another thought I'd like a bit of explanation why this is needed and a good thing. I'm not sure the possible benefits outweigh the potential confusion this can cause if a theme's styles target another.

[LuomaJuha]

Reverted the changes for theme-specificity, as it could have caused confusion, but left the _componentClass to be used later for overwriting styles

[demiankatz]

Thanks for the simplification, @LuomaJuha! Just one last documentation-oriented suggestion below.

[demiankatz]

Thanks, @LuomaJuha -- looks good to me, and all tests are still passing.

I can't merge this without dismissing @EreMaijala's open review, so I'll wait and see if he has any final thoughts before finalizing the work.

[LuomaJuha]

Sure!