Improve version strings

[Jaroslaw Staniek]

Hi,
Only on release, the CALLIGRA_VERSION_STRING in
libs/main/calligraversion.h is updated. However the following commits
are related to next version. This may be misleading for people testing
and reporting bugs (they see, say, alpha version in the UI but it's no
longer alpha but rather pre-Beta).

I propose extend our checklist/workflow to have extra change with Pre-
suffix and always commit it immediately after the tag.

Whenever I am doing screenshots in the Pre- period, it shows
misleading version info.

I am also proposing increasing numeric versions just after release, so
if someone pulls (unreleased) code with extra commits, it will at
least not be marked with previous version but with the next version,
which is IMHO a better choice and indicator.

Example:
1. on Alpha release: CALLIGRA_VERSION_STRING set to 2.6.0 Alpha

2. immediately after Alpha release: CALLIGRA_VERSION_STRING set to
2.6.0 Pre-Beta, and update numeric versions in CALLIGRA_VERSION_* to
beta

3. on Beta release: CALLIGRA_VERSION_STRING set to 2.6.0 Beta

-- 
regards / pozdrawiam, Jaroslaw Staniek
 Kexi & Calligra & KDE | http://calligra.org/kexi | http://kde.org
 Qt Certified Specialist | http://qt-project.org
 http://www.linkedin.com/in/jstaniek