Provide configuration from a conf file

Following guidelines provided by Flask documentation:

http://flask.pocoo.org/docs/0.10/config/#configuring-from-files

API_SERVER_SETTINGS env var can point to a deployment settings file.
Add update_message REST function
Implement MAPIStore support for set_read_flag
Merge pull request #155 from sixstone-qq/ejhernandez/rest-server-conf-file

Provide REST server configuration from a conf file
[pymapistore]: Add sanity checks when listing capabilities and remove a segfaulting `talloc_free`
[pymapistore]: Remove out of range check in delete_attachment (attachment IDs aren't necessarily sequential anymore)
[mapistore-python][rest.py]: Use MAPIStore table types and errors instead of magic values
[mapistore-python][rest.py]: Remove unnecessary temporal dictionaries
[mapistore-python][REST]: Correct argument modification
[mapistore-python][REST]: Name corrections in message tests
[mapistore-python][REST]: Correct trailing commas in kissDB
[mapistore-python][REST]: Correct `_encode_restrictions` (naming & return value)
[mapistore-python][REST]: Add description of the parameters in kissDB.py
[mapistore-python][REST]: Implement `messages_id_exists` in api_handler.py
[mapistore-python][REST]: Add attachment POST operation
[mapistore-python][REST]: Add attachment PUT operation
[mapistore-python][REST]: Add attachment GET operations (get attachment from ID & get attachments in a message)
[mapistore-python][REST]: Add attachment HEAD operations (check attachment exists & get number of attachments in a message)
[mapistore-python][REST]: Add attachment DELETE operation
[mapistore-python][REST]: Implement create_attachment + attachment class
[mapistore-python][REST]: Implement attachment_save & modify message_save