More PleineLune bugfixes & theming

Hi Piwik team !

This PR contains some bug fixes: 

* SegmentEditor > missing the "Add new segment" button in Zeitgeist (when there are 10 custom segments)
* Enlarge the clickable area of the Site selector
* SegmentEditor > when editing a segment, the text overlaps with icon. Also there is some remaining pixels on the top left.
* API + Widgets pages > Site selector missing

And some PleineLune theming:

* Map > Theme 
* jQplot > Metrics picker above graph not themed
* Period Selector > Calendar is not themed
* Login form not fully themed
* Visitors > Visitor Log > Tooltip not themed (eg. Hover on one Action)
* DataTable > on Hover on a datatable Column name, the Tooltip with documentation is not themed
* DataTable > Referrers > Overview. In the table of reports on the left, The list of reports appear on white backgrounds.
* All Websites > First column looks OK but other columns have white border around cells
* Admin > yellow tooltips are not themed (eg. in Geolocation)
* Admin > H3 style is not themed(eg in Admin>DB Usage)
* Annotations > Edit one. Save + Cancel buttons not themed. (buttons also used in Admin, Email reports, etc) 
* Visitor > Custom Variables > Click on a custom variable. The subtable loads. This table has alternate styles. The dark grey font color has not enough contrast. 

Cheers,
Thomas.