webadmin,userportal: Improve GIN bindings/injections

1. added BaseSystemModule.bindTypeAndImplAsSingleton
   method and used it for following bindings:
   - place manager
   - all resources (constants, messages, etc.)

   i.e. injecting CommonApplicationConstants and
   app-specific ApplicationConstants now yields the
   same singleton (ApplicationConstants) instance

2. modified classes to inject ClientAgentType instead
   of doing "new ClientAgentType" on their own

Change-Id: I09a0178171de3f4e698e616a78ca988f47436957
Signed-off-by: Vojtech Szocs <vszocs@redhat.com>