Text cells are only editable on double click.
Adds a useful method in AbstractRecodedLegend
It gets a key that is not already in the map from an original string.
prevents to put the same key twice from the UI
We use the dedicated method in legend to get an authorized key.
Adds some doc and remove unused imports
First version of the panel that creates a classification from scratch.
It currently does not much things : we ahve a group of radio buttons and
two JLabel that are activated or not and whos background colour can be
configured. Still missing the button that will be used to generate the
classification, coming in the next commit.
Adds the button that creates the classification
It makes a select distinct on the DS and builds a classification from
it. There are two modes :

- everything is copied from the fallback, color included
- everything is copied from the fallback and the colour is interpolated.
Typo in the javadoc
A JDialog is displayed when creating the classification.
It can be used to cancel the current Job. Note that this currently
causes two problems :
- The cancle operation can't cancel the opening : we can't listen
  to the status of an open operation on a DataSource... I'll have to
  write the retrieval part another way
- The current code prevents the application to shutdown properly.
  Concurrency is probably implied...
Improves classification creation
It is both more efficient and cancellable. Indeed, we now do a loop
through the whole DataSource that is faster than the select distinct.
And by performing a loop, we are able to stop it whenever we want.
Keeping the progress bar while feeding the RecodedLine
This way, when dealing with a field with a lot of different values, the
user is still able to cancel the process...