Remove unneeded selectors, share font-family definitions
Share styles between zoom & extent control
Make fullscreen control use shared styles
use button elements and add tooltips to zoomcontrol
use button elements instead of anchor elements and add tooltips to zoomcontrol
Better integration of button tooltips
Use «em» for buttons sizing
Make zoom control tip texts configurable
Coding style
Make zoomToExtent control use <button> instead of <a>
Add an alternative algorithm for zoomify tier size calculation

Zoomify uses a different algorithm than ol3 to calculate the number of
tiles per tier.
These algorithms are compatible in most cases, but they will lead to
different results with some particular image sizes.

This update provides an option for the zoomify source to use one of
these two algorithms.
Fix handling of the color cache
Merge pull request #1730 from elemoine/colorcache

Fix handling of the color cache
Use shorter syntax for integer division by 2
Make Fullscreen control use <button> instead of <a>
Minor cleanups
Use «em» based positioning
Css tweaks for touch devices
Restore `preventDefault` call that shouldn’t have been removed
Wording in description