Changes to locate site-config

With this commit the system for locating the site config file is as
follows:

 1. During the configure process cmake will create a file site_config.py
    in the build/python/ert_gui directory, the content of this file will
    be:

        config_file = "${SITE_CONFIG_FILE}"

     where ${SITE_CONFIG_FILE} is the variable set during the configure
     step. The generated file will be installed alongside the gert_main
     module.

 2. The gert_main module tries to import the site_config module and uses
    the config_file setting from there.

 3. If the ERT_SITE_CONFIG environment variable has been set that will
    take presedence.

With these changes it is not necessary for the frontend script to set
the ERT_SITE_CONFIG variable.
Fix windows compilation - location of variable declaration.
Merge pull request #586 from joakim-hove/site-config-build-fix

Changes to locate site-config
Merge pull request #587 from perroe/windows_compile_fix

Fix windows compilation - location of variable declaration.
Removed extraneous @TYPE@_vector_resize()
Merge remote-tracking branch 'upstream/master' into sensitivity_study
ERT-742 Fix the loading of the generated site_config.py file.
Merge pull request #589 from flikka/ERT-742-site-config

ERT-742 Fix the loading of the generated site_config.py file.
ERT-735 ERT-716 Adding parameter types to sensitivity study, other than GEN_KW.
Merge remote-tracking branch 'upstream/master' into sensitivity_study