Make pkg manager case-insensitive to wgt backend installer name.

Make pkg manager case-insensitive to wgt backend installer name.

[Issue#] WEB-3480
[Problem] Pkg manager cannot find backend installer for widgets with
file extension not being in lowercase.
[Cause] W3C P&C specifies that widget file extension should be matched
case-insensitively to string ".wgt". However, pkg-manager when resolving
backend installer for specific file matches its extension case-sensitively
against the backend installer names. In a result, if a widget file
extension differs from "wgt" (in letters capitalization, e.g. wgT, WgT)
pkg manager cannot find appropriate backend installer.
[Solution] Because other backend installers may require matching
their names case-sensitively the fix is to provide symbolic links to wgt
backend installer in all possible combinations of uppercase/lowercase
letters.
[SCMRequest] N/A

Change-Id: Ic146c96df7f22196af0f933045b442ef5d17babe