New parameter `$background-hover` added to `scss` style file.
Fix wrong class on selected months and years (`pmu-today` instead of `pmu-selected`)
update pickmeup.js

added defaultDate
this date will be displayed with an empty value
added default-date

this date will be displayed with an empty value
Merge pull request #46 from hapcoun/master

`default_date` option added
Two fixes:
* Fix for `$background-hover` default color
* Fix for resetting interval to 1 date with combination of `flat:false` and `hide_on_select:true`