gatt: Rename add_attribute to local_database_add
gatt: Add remote_database_add()

This patch adds a common function to insert an attribute in the
remote database mirror.
gatt: Avoid unneeded find info transactions

Discover all characteristic descriptor without inform the proper
characteristic handle range returns unwanted results. Services,
characteristics and other declarations should be ignored. This patch
implements an intermediate solution to avoid get unwanted attributes.
Final solution should be completely sequential to probe the profiles
when the all descriptors are discovered.
gatt: Add gatt_device struct

This patch unify GAttrib and database hash tables in one single hash.
IAS: Move D-Bus signal emit code to a separate function
IAS: Only emit property changed D-Bus signal if alert value changes
IAS: Use error() for invalid characteristic value
IAS: Emit "none" alert level if monitor/locator writes invalid value