Implemented Google auth API

Summary

With this release you are now able to share files and folders to individual users via their Google email address.

Using this feature

If you would like to use this feature then you must obtain a Google OAuth 2.0 Client ID. You can read on how to do that here.
When creating your Google OAuth 2.0 Client ID set the Authorized JavaScript origins to your fully qualified domain name and set the Authorized redirect URI to your FQDN/<path_to_site>.
Once you have obtained these details update your configuration with your client ID, you can do this by running the update script described below, or you can set it manually in the configuration file under _assets/configuration/config.json -> gapi.client_id = <your_client_id>.

Updating

To update the program, download the latest release from this repository and place the archived folder named dist.zip in the root of the directory where your current install is located.
Then run the following command to update the program:

unzip -o dist.zip
cp -r dist/* ./
rm -rf dist

If any configuration or database changes are required there will be a script located in _updates that you will need to run named <old_version>_to_<new_version>.php.
This can be done as seen in the following example:

php _updates/1.0.0_to_1.1.0.php

You may be prompted to enter some values when running these scripts.
If the installation fails then you may need to manually install the updates.
Currently there is no easy way to manually update the program as it will require you to read the source code and manually update the files. However in the future I may, if possible, comment the manual steps needed if the script fails.
Note: It is important that the update scripts are run in the correct order. For example if you are on version 1.0.0 and you want to update to version 2.0.0 and there are update scrips for 1.1.0 and so on then you should run those scripts first. If your old version is newer than the oldest version named on an update script then run the latest update script, for example if your previous version was 1.0.5, your new version is 2.0.0 and the latest update script you have is 1.0.1_to_2.0.0.php then you should run this script.
Note: It is also important that the update scripts are not run more than once as it may cause unexpected behaviour and break the program.

Full Changelog: 1.0.1...1.1.0