New function (and fixes) for management sections.

The file ./NSIS/FusionInventory-Agent/Include/SectionFunc.nsh has
this new function.

 * UnselectAllSection

Also, some other macros are converted to functions and some fixes are resolved.
Fix function 'GetCurrentInstallLocation'.

Function 'GetCurrentInstallLocation' is located in the file
./NSIS/FusionInventory-Agent/Include/RegFunc.nsh
Check value constrains for options /installtasks and /no-task.

This commit references #2011.
Save previous installed tasks for 'from-current-config' installation type.

This commit references #2011.
Synchronize NSIS sections with the /installtasks option.

This commit references #2011.
Cosmetic changes in the help.

This commit references #2011.