Fix PHP warnings, notices and errors

[MetalCar]

Hi there,

this project is exactly what I need, so I installed it and there come little PHP errors up.
I fixed them on a very very simple way so that other can use it directly withouth fixing errors or fully configurate that project.
I hope that is ok.

[tomershvueli]

@MetalCar Thanks for your PR into homepage! This looks good and I like the idea. Let's just fix up one thing before we merge it - can we have the error.php page have a map of error_codes with their text (right now it'll only have config_missing or something similar), and pass along the error code to the page, instead of passing an entire message through parameters? After that I'll merge it in!

[MetalCar]

This is my solution to make it possible to add more error-codes and show them.

BTW: It's possibly that I will add a second PR to seperate php logic and template, if it's okay.

[tomershvueli]

Instead of actual Enum's, let's simplify by doing something like this:
define("CONFIG_NOT_FOUND", "The config.json file wasn't found.");
Then we can get rid of the BaseEnum and translation files.