Add more methods to file connectors

[derNiklaas]

Planned changes:

• Test if folders exists
• Test if files exists
• Delete files
• Delete folders
• Fix a bug that occurs when trying to create a folder inside a non existing folder

[sebinside]

• Delete files, delete folders
• Test if file exists, test if folder exists

[sebinside]

WIP or ready-to-be-merged? Testing could be done from @joblo2213 :)

[derNiklaas]

I finished all the todos i had planned to do. If you don't have any further ideas on what to add/change, you can merge it ^^

I tested the following things:

• Creation of a folder inside a folder
• Creation of a folder inside a folder inside a folder inside a folder
• Test if a file & folder exists
• Deletion of a folder and a file