Support GM.* functions

[Aradiv]

The IITC-Button is lacking Support for the GM.* functions.

This means all Plugins that are using them don't work in IITC-Button

The GM.* function is commonly used to store credentials or make requests to do stuff like syncing with a backend server in a defined way so other plugins can't access them.

Without them the only other option is store them in a shared area where all scripts can access them.

Thats why IITC-Button should get a proper GM.* support especially:

• Value Handling
  • GM.getValue
  • GM.setValue
  • GM.deleteValue
  • GM.listValues
• HTTP Requests
  • GM.xmlHttpRequest
  • GM.getResourceUrl

[modos189]

Done in #40

[johnd0e]

@Aradiv
Does that work for you?