Add a check for db schema version

nipapd should refuse to start if the PostgreSQL db schema version is
outdated.

The up-to-date schema version (required to run) is stored inside
nipap/__init__.py
The current schema version is read out of the database comment.

The web-ui ( /version ) will also show the schema version.
Merge pull request #567 from dosomder/cli/422-fix-tab-completion

cli: Don't use colon as delimiter in tab completion
Add support for Ubuntu 14.04

.. by having nipapd depend on postgresql-9.1-ip4r OR postgresql-9.3-ip4r
instead of just on the 9.1 package. Should perhaps also work on Debian
unstable (which seem to feature both postgresql-9.3 or 9.4).

Fixes #568.
Merge pull request #569 from plajjan/568-fix-postgres-depends

Add support for Ubuntu 14.04
Further improve CLI "colon" tab completion

This changes the way tab completion works with regards to colon.

Given we have VRFs 123:123 and 123:456. Before change would yield
$ nipap address add vrf_rt 123:<tab>
$ nipap address add vrf_rt 123:123\:
Which is clearly broken. However this works:
$ nipap address add vrf_rt 123\:<tab>
123:123 123:456

While after the change, we fix the first behaviour
$ nipap address add vrf_rt 123:<tab>
123 456
But the completion lists only the part right of the colon and not the
complete VRF RT, which could be perceived as incorrect.

Kind of part of #422.
Update NEWS file
Merge pull request #488 from dosomder/460-check-db-version

Add a check for db schema version
Update contribution guidelines and license

The contribution guidelines have been cleaned up as well as parts of the
README file. Thanks to the Bootstrap team which has written such an
excellent CONTRIBUTING.md file that I just had to copy some (a lot) from
it. Documentation is licensed under creative commons. This wasn't very
clear before, but it is and now we have a docs/LICENSE file to prove it
;)

Also add the latest fixes and features to the NEWS file.
Bump version to 0.26.3
Fix notes on release handling
Fix editing of VRF in web UI

Used the wrong input name.

Also make statistics JS conditional to prevent javascript error.

Fixes #575.
Disable Travis-CI pylint and S3 upload test

We want pylint results over time and the running of pylint together with
uploading the results to S3 was a step in that direction. Recently we
found Scrutinizer-CI which can achieve the same things and as the
Travis-CI build process is considerably lenghtened by the S3 upload, I
have now disabled that test. We will rely entirely on Scrutinizer-CI!

Part of #274.
Merge pull request #576 from plajjan/575-fix-vrf-edit

Fix editing of VRF in web UI