Darken the offcanvas mask.
Elevate the offcanvas toggle above the offcanvas mask.
Fix offcanvas width at 240px for mobile.
Slow the transition and ease-in-out.
Transition the opacity of the offcanvas-mask.
Updated mask transition to ease-in-out
Updated offcanvas-width variable default to 240px, use variable
Leave offcanvas as display block so hide animation completes, position off screen with enough room for box shadow
Import default template variables into earthquake variables (for reuse)
Make earthquake theme extend default theme
Update usage for previewing earthquake theme
Merge pull request #67 from jmfee-usgs/ehunter-usgs-offcanvas-tweaks

offcanvas, earthquake theme updates
Update offcanvas-toggle to use menu text instead of hamburger icon. Style as a button.
Add background color incase linear-gradient is not supported.
Add active state to menu button.