Resize from edges

[andreybutenko]

This PR addresses #69, enabling windows to be resized from any edge or corner.

I'm new to contributing to open-source, so please let me know if you have any feedback -- I'd be happy to implement changes.

Some details:

• Add Window class variable _mouseEdgePosition that provides information on what edges the mouse cursor is hovering over.
• Add Window class getters for mouseOnWindowEdge, resizingHorizontally, and resizingVertically.
• Add Window class method startResize(e).
• Add CSS classes to window which changes cursors according to what direction the window can be resized towards.
• Sensitivity of what's considered an "edge" can be adjusted.

[rlamana]

@andreybutenko Please resolve the conflicts.

These problems with the dist files should be solved once the branch v0.3.0 is merged. This is a branch where I have been working on a migration to webpack and upgraded a little this old code.

[danimesq]

@rlamana, is this PR still valid merging by solving the conflicts?