Fixes #120, DatePicker test failures
Minor NavBar fixes
NavBar: Hide scrollbars in firefox and chrome
Add LESS mixins for flexbox

Browsers implement flexbox in several different ways (different attribute
names and values). This change adds LESS mixins to abstract away the
differences in flexbox syntax across browsers. This change also:
  - Adds unit tests for the mixins
  - Modifies the grunt tasks to compile LESS files in the tests directory
Fix #6: Switch NavBar from grid to flexbox

NavBar uses CSS grid which only works in IE. Specifically:
  - In NavBarCommand, CSS grid was used to ensure that each command's
    label shrinks by the right amount when icons and/or split buttons are
    enabled.
  - In NavBar, CSS grid was used to position the NavBarCommands.

Both of these uses of CSS grid were switched to flexbox to achieve
identical layouts.
Redoes the WinJS TabContainer to properly manage tab inside of virtualized collections (FlipView + ListView). Instead of relying on the IE-only event onbeforeactivate, this new implementation listens to tba key presses and, using a TreeWalker, runs through the child element of the TabContainer to determine if tab should continue on, or be bumped outside of the contained region.
Updated symbols.ttf to include more icons (v 1.0.3)
Fixes grouped alayouts for IE10 by using flexbox mixins in the stylesheet to automatically get the right flex styles
Cleaned up VS solution/project files.
Added .less files that got dropped from the previous .jsproj update.
disabling failing listview/listviewintegration tests
Fix #232 by moving WinJS.UI.CountResult out of VDS.
Move hub to use LESS flexbox mixins
Move hub from grid to flexbox
Prevent chevron from wrapping in Firefox

When putting 2 elements in a button styled with display:flex flex:row,
Firefox renders the elements in the same column rather than the same row.
This breaks the visuals for the hub's interactive headers (the chevron
appears under the title rather than next to it).

This issue is worked around by adding an extra div inside of the button.
The button's flex styles and children are moved into this div.
Reset margin on buttons for webkit.
Tweak text padding on input fields, fix placeholder color in webkit
Fix bug with select:hover
Add webkit styles for input range
Style progress element correctly in webkit