git: Remove the story branches stuff

It is no longer needed since we don't put story IDs into the branch
names any more.

Change-Id: cfcb66ea19
Story-Id: SF-77
git: Add StoryIds function, fix and improve stuff

StoryIds returns the list of unique non-empty Story-Id tag values for
the given list of commits. In case the tag is "unassigned", it is
ignored.

Change-Id: 7d173d356e
Story-Id: SF-77
prompt: Extract story listing in ListStories

Change-Id: 6c0181f1c6
Story-Id: SF-77
scripts: Add validation to LocalConfig

Make scripts.{get,set}_version a required config field.

Change-Id: 936f90c405
Story-Id: SF-77
version: Add functions to get from/set for branch

GetByBranch can be used to get the version string from a branch.

SetForBranch will set version for the given branch.

Change-Id: ebdf1d362d
Story-Id: SF-77
releases: Add a package with release utils

For now there is just ListNewTrunkCommits, which can be used to get the
commits that were added since to trunk since the last release tag.

Change-Id: 0af59af656
Story-Id: SF-77
Some silly file renaming

Change-Id: 9fb00c1a12
Story-Id: SF-77
jira/client: Add Client.Projects.ListVersions

Change-Id: 6eedff5c3d
Story-Id: SF-77
modules/jira: Add some API calls utility functions

Change-Id: a11cfde7c6
Story-Id: SF-77
Implement release start for JIRA

This change consists of two parts:
  1) Update commands/release/start.go
  2) Implement the common.NextRelease interface for JIRA

The steps should follow (but perhaps in a slightly different order):
  1) Make sure the repository is clean, i.e. there are no files that are
     tracked and modified.
  2) Make sure the remote repository is fetched and develop is up to
     date.
  3) Make sure there is no release branch in the repository.
  4) (JIRA) Fetch JIRA version associated with the version string as
     committed on the trunk branch since this is going to become the
     release version now.
  5) (JIRA) Walk develop to get the additional stories to be assigned
     into the next release. These are the stories affected by commits
     since the last release tag.
  6) Prompt the user to confirm these stories and the whole release.
  7) Create the release branch on top of develop.
  8) Commit NEXT as the version string into develop. In case NEXT is not
     specified, auto-increment the current trunk version string.
  9) (JIRA) Add the issues detected on develop into the relevant JIRA
     version.
 10) Push the modified branches.

Change-Id: e2f5a318d1
Story-Id: SF-77