Add tooltips

[alukach]

Helpful tips should appear when hovering over Menu operations. The tooltip data could be inputted when instantiating the operation within the menu. In the beginning, we could support only text. In the long run, I'd like to see richly-formatted helptext with the potential to add in illustrative .gif/.webm examples.

This can be done entirely with CSS and HTML, which is nice.

This was mentioned to some extent within #30 (comment)

[alukach]

An example of a clean CSS / HTML only tooltip: http://cbracco.me/a-simple-css-tooltip/

[mapsam]

OMG the attr() function in CSS is magical. I'll take this on, @alukach

[alukach]

Woah, that is crazy, I didn't notice that part before!

[mapsam]

This is currently being incorporated into geo-menu-updates branch. I'll make it more class-based so we can use throughout the app once that branch is ready.

[mapsam]

Tooltips have been added in #161 to the menu operations. They aren't necessary a unique component yet, but let's reopen when that comes up.

[alukach]

These look great! Agreed that these hover-tooltips along with the text in the clicked form (pictured below) totally suffice for the time being.

Notes for future:

• Would be cool to put a gif or webm with textual description visualizing the operation
• Can only get to the textual description when validation passes.