Fixed upgrade code to work with automatic plugin updates
Merge pull request #1 from pderksen/settings-layout

Settings layout
Moved upgrade code out of constructor; Fixed code to not load defaults if an upgrade is needed; Made sure to transfer uninstall_save_settings
Merge remote-tracking branch 'origin/master'
Added a constant PLUGIN_SLUG
Removed extra CSS file used only in settings-layout branch.
Updated links to internal settings pages to use...

PLUGIN_SLUG constant and add_query_arg() WP function to build
querystring values.
Brought in master to settings-layout branch.

Had to resolve conflicts on class-pinterest-pin-it-button.php via
Tortoise Git. Probably a better way to do this in the future.