Adds a comparator in a MappedLegend.
This way, we are able to consider String keys as Double keys when it
comes to sorting. Consequently, we can force a value classification made
on a numeric field to be coloured and sorted in the UI according to the
Double order rather than to the lexicographic String order.
Related to issue #478
Translate most of the Simple Style Editor UI.

Fixes #485.
Translate analysis types.

Note 1: For (Area|Line|Point) Symbolizers, I was able to translate in the
Advanced Style Editor when adding a symbol, but I wasn't able to
translate the default symbol in the Simple Style Editor or the Advanced
Style Editor. I'm not sure why. Maybe these strings are defined in .se
files somewhere, where they can't be translated?

Note 2: There are a lot of additions since apparently the translation
keys for legend and orbisgis-core had never been generated.
Fix spelling error and update translation
Values are now sorted even when opening the simple style editor.
We have now a special treatment for AbstractRecodedLegend while
initializing the SSE.
Simpligy some code, stop hiding an NPE.
Remove suspicious return null
Merge pull request #488 from agueganno/recode-value-order

Fix recode value order (fixes #478)

Values of the value classifications displayed in the simple style editor where sorted according to the string lexicographic order, even for numeric values. This PR tries to change that by offering the ability to give a dedicated Comparator to a MappedLegend. We use this feature to have a dedicated order when dealing with AbstractRecodedLegend whose classification is made on a numeric field.

Such a Comparator is given when:
* creating classifications in the editor
* computing the classification in order to open the editor so that the display is good on opening
Fix small translation errors
Merge pull request #487 from agouge/translation

Update FR translation after the Facelift series of PRs