A bit of constness.

Change-Id: If7681341c7d5d88286f36f943708f99b3c5700e0
(cherry picked from commit 0b5e5783d8b15b0415c9fd5043932882904aece8)
fdo#72125 - Expert config dialog takes too much time to come up

This is not a full fix, this just trims some of the fat in
CuiAboutConfigTabPage::FillItems.
Specifically
  - improve string handling
  - don't use catch/throw unnecessarily

Change-Id: I5b4987407bd007fbbb18f76fcf26f4a33282c0c0
Signed-off-by: Stephan Bergmann <sbergman@redhat.com>:
 reintroduced lost "/" into path of recursive FillItems calls

(cherry picked from commit 7468f9b773d5a9a4cb3af57cf123c2a0e7e937fd)
Do not create paths starting "//" when root is just "/"

Change-Id: If0b413a4fdd93465074548c7ea5451288c1d12aa
(cherry picked from commit bd8b3be0c7535e74ca8b63969be5c2bece0d3a3b)
More Expert Config Page fixes

Change-Id: Iaa2b7df4246ab3fa31737126f27e4a9da3814048
(cherry picked from commit 434465cee3c5e21881d3466f115d968e8fbf731c)