Introducing basic REST API

This is initial commit adding pecan/wsme framework.
Example operations are:
* GET /v1/project_groups
* GET /v1/project_groups/<group_name>

* GET /v1/projects
* GET /v1/projects/<project_name>

* GET /v1/teams
* GET /v1/teams/<team_name>
* POST /v1/teams
* POST /v1/teams/add_user

* GET /v1/users
* GET /v1/users/<username>
* POST /v1/users
* PUT /v1/users/<username>

* GET /v1/stories
* GET /v1/stories/<story_id>
* POST /v1/stories
* PUT /v1/stories
* POST /v1/stories/add_task
* POST /v1/stories/add_comment

* GET /v1/tasks
* GET /v1/tasks/<task_id>
* PUT /v1/tasks

More detailed documentation will be added later to a wiki page.

Tests will be added in a separate CR.

Auth stuff will be added in a separate CR after it is dicussed.

Change-Id: Ibace8cf7dd5bb933b0d2484b1d57b79bb8441a28