mod_base: Add 'filter_not' filter for inversely filtering a list
doc: Add documentation for 'filter_not' filter
mod_base: rename 'filter_not' filter to 'reject'
doc: Update documentation on 'reject' filter
mod_base: rename 'reject' filter to 'exclude'
docs: Update documentation on 'exclude' filter
Merge pull request #768 from mawuli-ypa/filter-not

Add exclude filter for inversely filtering a list.
Added Mawuli @mawuli-ypa to the list of authors/contributors.
core: Separate user sites, user modules and global config from the priv/ directory

Fixes #767

See https://github.com/zotonic/zotonic/issues/767 for the full
specification and discussion.

The zotonic.config file is now search for in $HOME/.zotonic/<version,
$HOME/.zotonic, /etc/zotonic/<version>/ and /etc/zotonic.

The directory where user-defined sites and modules are searched in are
now defined in the user_sites_dir and user_modules_dir config
variables. These defaults to $ZOTONIC/user/sites and
$ZOTONIC/users/modules, respectively.

The "zotonic enablesite" and "zotonic disablesite" commands are removed.

The compilation of zotonic is now handled in the zotonic_compile.erl
module instead of in the Emakefile (due to the variable nature of the
user_sites_dir we can no longer use an Emakefile with hardcoded paths).

Compilation of Zotonic is now done in a few parallel worker processes,
to speed it up.
core: small start adding prefix of site name to lager messages.
core: Global config file tweaks

- On startup, print out which global configuration files are in use
- Allow the Zotonic node name to dictate the path to the config files

See issue #767
core: fix z:m() in a running system
mod_base: add filter truncate_html.
Add 2nd argument to filter_truncate to define the break-off text.
mod_base: add filter truncate_html.
Add 2nd argument to filter_truncate to define the break-off text.
doc: add filter-truncate_html docs, document extra arg for filter-truncate.
Replaced some 'when'-s with 'if'-s.
Added placeholder for mod_editor_tinymce
scripts: Fix zotonic_install
mod_base_site: fix typo in divv tag.
core: make the zotonic_setup compatible with OS-X and BSD grep.
Issue #777
core: refactored parsing of config files.
Changed z_sites_manager:get_site_config/1 to return either {ok, Props} or {error, Reason}.
Added z_sites_manager:get_builtin_sites/0.
Don't try to start any sites in priv/sites, unless it is a builtin site.
core: hide the builtin sites from the zotonic_status overview.