CORE, RPC, GUI: loading configuration to GUI from RPC

CORE:
- Support for loading Properties as Map from custom
  configuration file.

RPC:
- Return Map<String, String> as configuration for GUI on
  special rpc request "/utils/getGuiConfiguration".

GUI:
- Removed some items from static configuration files.
- GUI configuration is always loaded after getting
  PerunPrincipal and GUI won't load without it.
- BasicOverlayType can be used to get any property
  from any JS object.
- PerunWebSession is used to store GUI configuration.
- Display captcha for default (non) URL even for devel.

- Custom logo can't be set during build (by maven) anymore,
  but is stored the same way as rest of GUI configuration.

BEFORE ACCEPTING THIS COMMIT TO PRODUCTION:

- Create file "perun-web-gui.properties" in /etc/perunv3. Perun-core currently
  doesn't support custom location for properties files it loads.

- Put following data in perun-web-gui.properties file:

perunReportEmailAddress=perun@cesnet.cz
defaultRtQueue=perun
vosManagerMembersGroup=members
isDevel=false
logoUrl=img/logo11.png
getSupportedPasswordNamespaces=einfra,einfra-services,egi-ui,sitola
getAttributesListForMemberTables=urn:perun:member:attribute-def:def:organization,urn:perun:user:attribute-def:def:organization,urn:perun:user:attribute-def:def:preferredMail,urn:perun:member:attribute-def:def:mail,urn:perun:user:attribute-def:def:login-namespace:einfra,urn:perun:user:attribute-def:def:login-namespace:meta,urn:perun:user:attribute-def:def:login-namespace:mu,urn:perun:user:attribute-def:def:login-namespace:sitola,urn:perun:user:attribute-def:def:login-namespace:cesnet,urn:perun:user:attribute-def:def:login-namespace:egi-ui,urn:perun:user:attribute-def:def:login-namespace:einfra-services
getAttributesListForUserTables=urn:perun:user:attribute-def:def:organization,urn:perun:user:attribute-def:def:preferredMail,urn:perun:user:attribute-def:def:login-namespace:einfra,urn:perun:user:attribute-def:def:login-namespace:meta,urn:perun:user:attribute-def:def:login-namespace:mu,urn:perun:user:attribute-def:def:login-namespace:sitola,urn:perun:user:attribute-def:def:login-namespace:cesnet,urn:perun:user:attribute-def:def:login-namespace:egi-ui,urn:perun:user:attribute-def:def:login-namespace:einfra-services