Merge branch 'hotfix'
Checks if the sortable key exists among admin-column properties. Fixes #35
Merge branch 'hotfix': v0.5.4, Fixes bug #35
Fixes #38
Adds CSS for datepicker
Fixes error in readme
Merge branch 'master' into development

Conflicts:
	README.md
	classes/class-wg-meta-box.php
Fixes #31, #34
* Puts the labels above the input fields when the container is in the sidebar
* Moves the library into a plugin in order be able to load assets
* Adds the constant WG_META_BOX_URL to specify custom URL for assets dir