Rename internal types in st2client from Trigger to  TriggerType

- This way the server and client types use identical names. The only place
  we distinguish is in the display strings. Long term should help avoid
  some confusion.
Add missing license header.
Add Trigger model to client and alias it as TriggerSpecification.
Add Trigger manager
getspecs subcommand on st2 triggers.

- Returns the Trigger specification that make up a concrete Trigger.
Undo unintended change.
TriggerSpecification to Trigger Specification
Merge pull request #905 from StackStorm/trigger-visbility-improvements

[RFR] Trigger visbility improvements
Fix absolute path for test fixtures

Add fixtures_pack to the join statement in the get_fixture_file_path_abs method of FixturesLoader.
Merge pull request #906 from StackStorm/STORM-910/fix-fixture-abs-path

Fix absolute path for test fixtures
Refactor mistral tests to use FixturesLoader

Remove antique fixtures and replace with the common FixturesLoader.
Merge pull request #907 from StackStorm/STORM-883/mistral-integration-tests

Refactor mistral tests to use FixturesLoader
Using wf trace logging config file for mistral logging.
typo Jinga -> Jinja
Merge pull request #909 from herveleclerc/master

typo Jinga -> Jinja
Fix a bug with sensors - we need to establish a database connection inside the
sensor_wrapper since sensor_wrapper runs inside a separate process.

We need to do this because of changes introduced in
931c238eac087ea84d535df1c3823edfbdfe8eb5
Merge pull request #910 from StackStorm/sensors_triggerwatcher_fix

Fix sensor exploding when TriggerWatching was reading existing Triggers from the database
Merge pull request #908 from StackStorm/mistral-logging

Using wf trace logging config file for mistral logging.
Move unit tests to separate directory

Move unit tests to tests/unit directory for each component. This is in preparation for adding integration tests. Modify test path in Makefile and tox.ini.
Throw better exception is a rule object is missing corresponding Trigger object.