SciDAVis - Improvements SVN-temp

- Fixed two-sided comparison in assert.

- Made importing of ASCII data as numeric values the default (on new
installations). Experience has shown that many users don't notice that the
data is being marked as "text" and complain about everything being plotted
as a straight line. If the new default leads to problems with importing
non-numeric data, at least it should be more obvious *where* things have
gone wrong.

- ported editable column date-time format from LabPlot svn rev. 172
(closes bug #2820102: There is no way to use custom date-time formats)

- More updates to Czech translation by Pavel Fric.

- Improved Czech translation by Pavel Fric.
- Lupdate of all translations.

update and completed reference chapter up to menu "plot"

update and completed reference chapter up to menu "plot"

- Applied patch #2849492 (Add close button to About Box).

html version more close to scidavis website look

- Eliminated some crashes and cases of "Couldn't change the axis type to the
requested format" when working with date/time axis labels.