Notification of string changes

Author: Marina Glancy
MDL-33550 Correctly process situation when file reference source is missing
- do not die with fatal error if source file in moodle internal repository is missing;
- moved code duplication for moodle repositories into class repository (functions send_file, get_reference_details, get_file_by_reference, get_file_reference);
- update file status after repository::sync_external_file so we know that it is missing (or not missing anymore). Do not run this function more than once for file within one request;
- display readable name for Private Files and Server files with the new format;
- display broken icon in filemanager if we know that source is missing, display information (for admin) where it was located before: see repository::get_reference_details() and extending classes;
- removed unnecessary queries in stored_file::sync_external_file();
- syncronize files before displaying it's size in mod_resource, do not query directly


http://git.moodle.org/gw?p=moodle.git;a=commit;h=0b2bfbd1c63eaff88e3ecbb9907321bd69dc4702
http://github.com/moodle/moodle/commit/0b2bfbd1c63eaff88e3ecbb9907321bd69dc4702

+ 2.3 en [lostsource,core_repository]
+ 2.3 en [privatefilesof,core_repository]
+ 2.3 en [undisclosedsource,core_repository]