includeEtcEntry: New dictionary include directive: #includeEtc "etcFile"

Description
    Specify an etc file to include when reading dictionaries, expects a
    single string to follow.

    Searches for files from user/group/shipped directories.
    The search scheme allows for version-specific and
    version-independent files using the following hierarchy:
    - \b user settings:
      - ~/.OpenFOAM/\<VERSION\>
      - ~/.OpenFOAM/
    - \b group (site) settings (when $WM_PROJECT_SITE is set):
      - $WM_PROJECT_SITE/\<VERSION\>
      - $WM_PROJECT_SITE
    - \b group (site) settings (when $WM_PROJECT_SITE is not set):
      - $WM_PROJECT_INST_DIR/site/\<VERSION\>
      - $WM_PROJECT_INST_DIR/site/
    - \b other (shipped) settings:
      - $WM_PROJECT_DIR/etc/

    An example of the \c \#includeEtc directive:
    \verbatim
        #includeEtc "etcFile"
    \endverbatim

    The usual expansion of environment variables and other constructs is
    retained.