SciDAVis - Improvements SVN-temp

- Cleaned up build system. Added options for disabling some features which are
frequently undesirable when integrating SciDAVis in a Linux distribution,
such as checking for updates. Added presets for common setups (end user
installing from source, packaging, self-contained binaries) which can be
selected on the command line (e.g. "qmake PRESET=linux_package") without
having to edit/patch a configuration file.

- Changed link for Slackware packages (until linuxpackages.net gets updated again...).

- Fixed incompatibility with Qt < 4.5

- Simplified process of building SciDAVis on Windows.

- Reverted (accidental?) change in r764 causing peak detection to find the maximum *absolute* value. The resulting behaviour is a bit confusing, to say the least.

- Fixed bug #2973098 (Data Reader broken for Dates as x) and related problems.
In particular, DataCurve::tableRow() was broken for DataTime values as well as
for columns with non-unique values. Screen picker and the tracker text of
data picker have been modified to use the same output format as the
bottom/left scales (currently hard-wired, switching to top/right would require
a user interface to be made up). The status bar output of data picker uses the
same format as the underlying columns of the selected curve.

- Tagging version 0.2.4.

- Version bump to 0.2.4.

- README for Windows installer synchronized with the nsi script.

- Compatibility table access functions modified so as not to use deprecated
methods.