Fixed BUG #12311. Changed ParaView version number policy.

We now use "git describe" to determine the version for ParaView. Thus we no
longer have to use minor/major version number trick for releases. "git describe"
returns a string such as "v3.10.1-1701-g427f283". The version is then set as
follows:
Major: 3
Minor: 10
Patch: 1
Full : 3.10.1-1701-g427f283

If Full=="Major.Minor.Patch", then it's treated as a release.

Release candidates can be tagged as "x.y.z-rcN" and the version will be set
correctly.

If git cannot determine the source version correctly, then
"CMake/.paraview.version" file is searched for and we try to parse the version
string from this file. It's a fatal error is both these approaches fail.