GWT: x.x, add concordance context cut

See #943

Currently “text” is the only structure used to cut concordance contexts.

We must be able to cut several structures (for example “text” or “plu” & “deplu” or “p”)
The import parameters defines which structures to cut in the concordance
- Step 1: add “context_limit” parameter to “import.xml” file.
  - default text value is “text”
  - default type value is "list" *** can contain multiple values (ex: "text,plu,deplu") *** if type=“list”, the context limit query will be []|[]|…|[]
  - if @type=“query”, text value must be a CQL query
- document how to patch “import.xml” for this parameter
- test with Apocalypse corpus
- Step 2: replace patch by complete import parameter interface
  - build an import UI for this parameter
  - save the field in “import.xml”

Add in admin documentation the new import parameter element : uis/ui@command=concordance/context_limit, @type attribute and text value

* Call concordance on GRAAL corpus with query "

[]"

* add the new import configuration in import.xml file (see Admin manual)of the GRAAL corpus

...
<uis>
  <ui command="concordance">
    <context_limits type="list">text,p</context_limits>
  </ui>
</uis>
...

* reload GRAAL corpus (no need to re-import and produce a new binary corpus with RCP ???)

* reload user session

* Call concordance on GRAAL corpus with query "

[]", ensure left contexts are empty

(from redmine: issue id 1093, created on 2014/10/22 by Matthieu Decorde)