Remove heredoc syntax from lang strings

AMOS threw exception mlang_parser_exception
when parsing heredoc
Add mod_lti dependency to local_mediacore version
Rename constants to avoid possible collisions

Rename MEDIACORE_PLUGIN_NAME to LOCAL_MEDIACORE_PLUGIN_NAME
Delete MEDIACORE_SETTINGS_NAME and use LOCAL_MEDIACORE_PLUGIN_NAME
  which were the same value in any case
Rename MEDIACORE_DEFAULT_SCHEME to LOCAL_MEDIACORE_DEFAULT_SCHEME
Update versions

Remove .files from all plugins
Update all versions accordingly
Update .gitignore

Ignore sub plugin README files
[changelog] Updated the plugin code as per Moodle.org
comments when reviewing the plugin. All minor non-breaking
changes.
Merge branch 'fix-plugin-review-suggestions'