dos2unix/less/screen/terminology/tree: Social&Content -> System or Platform Development

dos2unix/less/screen/terminology/tree: Social&Content -> System or Platform Development

These packages do not belong into "Social & Content". Opinions differ
whether they belong into "System" or "Platform Development".

dos2unix and less were discussed without a final resolution in TINF-427.
This commit proposes to include them in "System" because more people
voted for that and there might be cases where normal users also need
these tools.

screen/terminology/tree get moved to "Platform Development" as
requested by Mikko. I am fine with that, because the deciding "who is
it for" question can be answered either way.

Change-Id: I031d16f935f7256ab00c884adb3b5d0c46f58a79
Signed-off-by: Patrick Ohly <patrick.ohly@intel.com>