[MERGE] [REF] crm stage management cleaning

[REM] base_stage removal

Using stages and states is not easy to manage. Indeed those two fields mess with the same basic concept. This task remove the state on crm.lead and crm.claim models, leaving only stages.

Main features:
- removed base_stage inheritance on crm.lead and crm.claim models
- removed state field on crm.lead and crm.claim models
- removed state field on crm.case.stage model
- added date_last_stage_update on crm.lead and crm.claim models, holding the date of the last stage change, allowing reporting and analysis on time spend in stages
- date_open is set when assigning an user to the lead / claim; date_open now means assignation date

This allows nearly to remove all buttons on the form view, leaving only a dynamic stage management using the statusbar. On opportunities, Mark Won / Lost are kept.

Subtypes have been updated :
- new: stage_id.sequence=1
- stage changed: stage_id changed, not new
- user assigned: when user_id is set

This branch is the last one removing state where stage already exits. There is no need anymore of base_stage that is removed.

Misc:
- [IMP] views accordingly;
- [IMP] reports accordingly, added date_last_stage_update in reports;
- [IMP] subtypes;
- [DOC] doc directory + changelog + stage explanation in crm_lead

bzr revid: tde@openerp.com-20130812120725-u10zptg2m4z8ah4k