Generate poll-urls via model_url

Fixed Bug to wrong poll urls
Fixed #823
Start Browser on custom IP, fixed #827
Merge pull request #832 from normanjaeckel/Fix_Start_Option

Start Browser on custom IP, fixed #827
Merge pull request #831 from ostcar/issue-823

Generate poll-urls via model_url
Added Czech translation (Thanks to Pavel Fric!)
Merge pull request #835 from emanuelschuetze/czech-translation

Czech translation
Fixed tooltip and duration in agenda.

The tooltip did not show the end of an agenda item, but of the hole event.

If a item was closed, it was not used to calculate the end of the event.

Fixed #833
Use get_active_version in motion.__unicode__()

Fixes the bug, that motion.__unicode__() raises an AttributeError, if the active_version
was None.

Fixes #822
Merge pull request #830 from ostcar/issue-822

Use get_active_version in motion.__unicode__()
Merge pull request #836 from ostcar/issue-833

Fixed tooltip and duration in agenda.
Disable deleting active versions of a motion
Merge pull request #837 from normanjaeckel/issue-822-additional-new

Disable deleting active versions of a motion
Add paragraph around each motion version warning (to show each warning in one line).
Merge pull request #840 from emanuelschuetze/motion-version-warnings

Show each motion detail version warning in one line
Fixed #833
Merge pull request #841 from ostcar/issue-833

Issue 833
Update CHANGELOG and INSTALL
Merge pull request #842 from normanjaeckel/CHANGLOG_1.4.1

Changlog 1.4.1
Release 1.4.1
Update version to 1.4.2-dev