SciDAVis - Improvements SVN-temp

- fixed bug #2710488: Undoing conversion to text column broken

- added Piwik code

- Implemented a more sophisticated file-saving protocol, which is supposed to
protect against data loss in the event of a system crash shortly after saving
the file.

Previously, there was a problem with modern Linux filesystems like ext4,
which could lead to a zero-length project file after a crash. For details,
see here[1].

Instead of writing a backup copy and then overwriting the original file, we
now follow the procedure given in [2]:

1) save the new file as <filename>.new
2) make sure data is actually written to disk (fsync)
3) rename <filename> to <filename>~ (keep backup copy)
4) rename <filename>.new to <filename>

Note that the newly written data can still be lost by a system crash with
some bad luck, because changes to the directory containing the file aren't
synced. However, seeing that working on a project happens in memory most of
the time, there'll always be plenty of chances for a system crash to cause
data loss. The point of the above change is rather that after a system crash,
either the old or the new version of the file should be on disk, so you loose
at most the work done since the last saved state. This is also what Vim, Emacs
and other applications do.

[1] http://beta.linuxfoundation.org/news-media/blogs/browse/2009/03/don’t-fear-fsync
[2] http://bugs.launchpad.net/ubuntu/+source/linux/+bug/317781/comments/54

- implemented update of columns list in formula tab on column add/remove

- removed non-functional option "Fit curve # pts" from PolynomFitDialog

- Fixed crash when sorting columns separately.
- Fixed several problems with adding error bars from data percentage or
standard deviation.

- Fixed selection of Gauss, Lorentz and Polynomial fits in fit wizard with
translations. Closes bug #2691956.

- Fixed Table::text() and Table::setText(). Particularly, opening legacy files
with non-numeric data was broken.
- Fixed differentiation filter.

- fixed crash when selecting a deleted file from list of recent projects

- reverted r1088 (labels were meant to contain the user-visible e/E)
- added missing tr() for "Fill Selection with" and ran lupdate
- fixed multiple usage of Alt-A shortcut in German translation of PlotDialog