Moved /classes, /functions.php, /base.php, /site.php, /api.php, /database.php, /error_handling.php  to /core
Moved /galery/index.php -> /core/gallery.php
Splitted config.php into config.php,
/core/config/system_config.php,
/core/config/system_config_2.php.

Moved /admin/backups -> /backups

Moved /plugins/site_users -> /core/plugins/site_users
Created plugin /core/plugins/config

New class PC_model: used for getting data from entity main ant content tables.
New class PC_debug: used for debugging, logging, time measurement. PC_base extends PC_debug.
New class PC_utils: from plugins/utils/class.utils.php class PC_Utils. (#138)

Fixed issues: #128, #169, #173, #166.

Added per page user access settings. All admin page operations are now secure.
New config setting: $cfg['router']['no_trailing_slash'] (boolean)
Permalinks for pages.

More functions for page reference_id:
PC_page->Get_page_link_by_reference($reference, $ln = '')

Admin: 'page preview' function is available regardless of domains.

Hook observers:
$core->Register_hook_observer($event, $observer).
/admin/admin.php: cache is being cleared after creating/moving/saving page:
$core->Register_hook_observer('create_page', 'core/cache/clear');
$core->Register_hook_observer('move_page', 'core/cache/clear');
$core->Register_hook_observer('after_page_save', 'core/cache/clear');

Redirect in case of additional routes (if page has no controller)
for example page/foobar is now being redirected to frontpage,
but plugin_page/foobar is not being redirected.

Plugin admin api automatic handling:
PC_admin_api.php is not needed.
It is enough to place api class (which extends PC_plugin_admin_api) file in /admin_api/ directory of the plugin:
plugins/pc_shop/admin_api/PC_shop_products_admin_api.php
For example in case of api call /admin/api/plugin/pc_shop/products/move,
PC_shop_products_admin_api::move() is being called automatically.
Merge branch 'master' of https://github.com/profis/profiscms