Users model added.

* findByUsername: Find a user by its username.

Change-Id: I82949312be743e5d4b956b6a5023deb77d037671
Method documentation.

* findByUsername: Documentation added.

Change-Id: I2e522074608b11eac19274ad762f2f67358e2063
Class refactoring.

* Users > Model_Users.

Change-Id: Iaf304e768b2d57422c8b3c7f18faa4d6d4ac41cf
Acl service added.

* Using singleton pattern.

Change-Id: I045925c08f1a20397c3e9146fb38496e8fcb080d
Resources model added.

* getForAcl: Get a list of resources for ACL querying.

Change-Id: Id95fe22e4738174b1db28e64d1a2e894708fa531
Method to get roles for ACL querying.

Change-Id: I219a48bb83df0cc223657d1b74b961661551ec97
Get table name from $_name variable.

Change-Id: Ibfabe52b82ca2fc8ae41c555d6a4f0f412ba16dc
Model to get privileges.

* getForAcl: Get a list of privileges for ACL querying.

Change-Id: Iee35697234b883c7894f0414599330c355c65a34