[IMP] add odoo.py shell subcommand

It starts an interactive Python console. If a database is provided, with the
`-d` argument `env` is bound to an Environement with the uid and context of
SUPERUSER_ID and `self` is bound to a RecordSet of the corresponding res.users.

Courtesy of Daniel Reis, reworked to be a bit more agnostic.

Command class is moved from __init__.py to command.py to improve imports of
__init__.py
[IMP] crm deduplicate contacts view

Move buttons to the footer.

Closes: #562
[IMP] SEO on product categories
[ADD] ir_actions add logging to server actions

The log(message, level='info') function will create ir_logging records, useful
to debug server actions.

Closes: #928
[IMP] account, restrict removal of accounts used on account.tax

Closes: #789
[IMP] ir.attachment access right, use write mode of related object

For related models, check if we can write to the model, as linking
or unlinking attachments can be seen as an update to the model.

Courtesy of Vincent Vinet

Closes: #1035
[FIX] server report_configuration database

Report unix socket instead of localhost when using named sockets.

Courtesy of Leonardo Pistone

Closes: #1899, #1900
[IMP] Cleanup and refactoring of exception handling

Unify and refactor exception handling in framework and addons.

The generic `except_osv` is now deprecated, and replaced by more specialized exception subtypes:
 - `UserError` (renamed from Warning, as it conflicts with the built-in `Warning`) raised when a non-technical error occurs during a business operation. It could be a missing information in the data provided by the user, or a misconfiguration.
 - `AccessError`: raised when any operation is denied because the user conducting it does not have the required access rights.
 - `AccessDenied`: raised when an operation that requires authenticated access is attempted via an unauthenticated request.
 - `MissingError`: raised when an operation is attempted on a record that does not exist.
 - `ValidationError`: raised when an operation violates a SQL or Python constraint.
 - All other exceptions are internal errors due to a system problem or bug, and raised untouched to the client-side, which should display a traceback.

All exceptions take a single message argument.

The `test_exceptions` module has been updated to showcase both new and old (deprecated) exceptions.

A great many old `except_osv` had a useless title with "Error!" or "Warning", those have been removed, as this is handled by the client-side widget that displays the messages.

This commit introduces a more consistent policy for logging errors and warnings:
 - All messages that do not require administrator attention should be logged at INFO level or lower. This includes all errors that are notified to the user in a friendly manner, even for access right problems or validation errors during business operations.
 - All messages that indicate a likely misconfiguration or malicious use by the users should be logged at WARNING level, as they typically require administrator attention.
 - All other unhandled internal errors cannot typically be handled by the user and should be logged at ERROR or higher level, as they require immediate administrator attention.
[IMP] Avoid blocking the browser when index.html is empty in static/description.
[IMP] To avoid raising a ParserError Exception when html contains a bad html format.
[FIX] When we compute the relevancy, days = 0 if the create_date doesn't exist.
[FIX] Raise UserError when bad html format for html2plaintext.