Correct icon classname for user image fallback

Without the "icon" class name, the fallback icon is not displayed properly.
Fix broken combobox pagination
Center pagination buttons regardless of listwidth
Add check for allow_url_fopen then CURL fallback

Add a check to see if allow_url_fopen is enabled then fallback to CURL if available.
Cleanup the resource getnodes processor

Prior to this cleanup, due to an issue with ltrim(), it was impossible for custom resources to use a custom icon. After this cleanup that ability is restored through a system setting (that 3PCs need to provide) of mgr_tree_icon_<CLASS_KEY> where <CLASS_KEY> is a lowercase representation of the class key with, if applicable, the "mod" prefix removed.

On top of that, this clean up also resolves duplicate classes being assigned to the icon. It also improves the readability and fixes some weird and/or duplicated logic.
Move OnInitCulture event to parser service

As described in issue #10366
Update phpThumb to v1.7.13
Enable usernav menus for mobile devices
Fix checking if connectors are included by a defined constant instead of a get_included_files() check.

This resolves an edge case scenario where a file that is automatically prepended (e.g. auto_prepend_file) causes the included check to fail as the connector.php is not the first file in get_included_files(). The entire manager becomes unusable in this case, as none of the AJAX requests work as expected.

The new check per this commit first checks the existence of a constant (which the other connectors define). As alternative, it also checks if the MODX_CORE_PATH is defined, which is a pretty good indicator that for example a third party connector loaded the main connector (as they can't find the connector location, without knowing the location of the core and loading the config file).
Fix long category name overflow in vertical tabs
Simplify Gravatar retrieval and fallback

Utilize Gravatar's built in fallback image so that we don't need to check for an existing profile image on every manager pageload.
Fix Files Tree Hover-Preview Thumbnail border not expanding to correct width
Fix password reset feature

Addresses #11725 for 2.3.x (master)
Do not output modScript include result w/o explicit string return

Addresses #11705
Update xpdogenerator.class.php
Fix excessive space in package update window
Adjust appearance of saving window
Fix labels / tvs in custom FC tabs
Simplify Gravatar profile image fallback

Merge remote-tracking branch 'origin/pr/11716'

* origin/pr/11716:
  Simplify Gravatar retrieval and fallback
  Add check for allow_url_fopen then CURL fallback
  Correct icon classname for user image fallback
Fix pagination on Topic combobox

Addresses issue #11713

Merge remote-tracking branch 'origin/pr/11720'

* origin/pr/11720:
  Center pagination buttons regardless of listwidth
  Fix broken combobox pagination