+ Implementing support for SMF-style file modifications (mods). (ManagePlugins.php, Subs-MinifyPHP.php, index.php)

@ Notes:

(1) You may only edit files loaded via loadSource, including SSI.php and most files in the core/app folder.
(2) This is a very basic implementation for now. Hopefully, I can build upon this to make it a better mod system than SMF's.
(3) You need to add a 'mods.xml' file to your plugin folder, and just have it say things like this: <file name="Home"><operation><search position="after">loadTemplate('Home');</position><add>echo 'Hello, world!';</add></operation></file>.
(4) You can use CDATA tags if you want, but they're not actually taken into account. Meaning you can't really use </position>, </add> and </operation> strings inside your code. But then again... Why would you?
(5) This new feature enforces the use of app caching. So every time you enable or disable a plugin, pages should take a bit longer to load, to give Wedge time to actually re-patch files on your behalf. Good news is, if a file can't be patched (e.g. wrong file version or you edited it manually), conflicting plugins should be automatically disabled, and an error will be logged for admins to look into. Needs translations and stuff.
(6) As usual, I haven't tested much.
Merge remote-tracking branch 'upstream/master'