Remove SolrCell support
Simplify document creation
In case of conflict, try later

If there is a conflict, trying later will solve the conflict by
either ignoring the task (old document) or executing it successfuly
(new document).
Remove useless date format

Date is automatically formated when placed in a document
Improve concurrent update with NRT

Use Near RealTime Search to do Optimistic concurrency, adding
the "_version_" field to the document ensure that the document hasn't
been modified between the "OudatedCheck" and the indexation of the
new version
Fix non-printable char issue with solr
Merge branch 'master' into search-1.3.x
Set the BASE_WAITING_TIME to 10ms

It will take only 8 more attempts before reaching the default
5 minutes waiting time and will avoid the case where a single failing
document in the queue slows down everything.

This isn't supposed to happen ofter, but if it does it would be better
for the TaskRunner to not stop for too long
Merge branch 'master' into search-1.3.x
Use long instead of int to mesure time
Reset the timer only when a task was successful

Currently the timer is reset after each iteration (thus repeats the
minimum wait every time).
Merge branch 'master' into search-1.3.x