Removed checkedItems field from GitProjectsImportPage

Removed checkedItems field from GitProjectsImportPage

The checkedItems field has been removed from GitProjectsImportPage,
and a getCheckedProjects method has been added instead, which computes
the set of checked projects based on information available from the UI
widgets.

This fixes at least one bug that was affecting my work: unchecking projects
by using the spacebar didn't work, because there was no KeyListener in place
to update the checkedItems field. This lead to the project being unchecked
in the UI, but still considered checked by the wizard page, and upon
clicking Finish, the wizard would try to import all of those unchecked
projects.

[ms]:
- split off extraction of ProjectRecord into separate change
- ported change to current master
- added Ryan's copyright

Bug: 308284
Change-Id: I5c0889e9f6e95c2c62d96195623499802ce701a1
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>
Signed-off-by: Ryan Schmitt <ryan.schmitt@boeing.com>