Merge github fork changes back to fusion repo

[jng]

I have made a temporary fork of the 2.2 branch some months ago in github

​https://github.com/jumpinjackie/fusion-multimap

This fork contains several major changes to improve legend performance and multiple Map Definition support and lots of usability tweaks for various widgets and the fusion core.

The legend changes alone would probably resolve most legend-related tickets filed thus far (#166, #388, #131, #244, #261, #400, #425)

This ticket is a tracking ticket to monitor all relevant submissions.

[zspitzer]

I would like to credit Hume City Council ​http://www.hume.vic.gov.au/ for funding this round performance work on Fusion

[jng]

All changes have been ported back