Add updated version of Redis modules

Add updated version of Redis modules

Adapted from Nokia internal RCP code repository, revision 120a6bb from
branch 'rcp2.0'.

Changes to original:
* Unit tests and checking for unit test dependencies is now disabled
  by default.
* Unit tests can be enabled with the configure flag '--enable-unit-test'
* Remove Nget and Ndel. These will be refactored and reintroduced in
  a later commit.
* Run valgrind in UT to check for memory leaks.
* For opaque types there is not need to use real redis types in UT.
  Instead define opaque types as dummy structs in
  'tst/mock/include/redismodule.h'.
* Add instructions on running UT to redismodule/README.md.
* Remove dead code and unused includes.
* Fix compiler warnings in UT.
* Treat warnings as errors in UT.

Signed-off-by: Arvo Heinonen <arvo.heinonen@nokia.com>
Change-Id: I8759d1c91d0dbd8c6373b7863ea11287e2d799c2