feat(forRoot): default configuration

[rbalet]

Description

Being able to pass default configuration to the forRoot() method.

Example

FroalaEditorModule.forRoot({
  key: FROALA_KEY,
  toolbarButtons: [TOOLBAR_BUTTONS],
})

Why ?

This would reduce the number of time we have to pass those values inside the html template.
It would also make it easier to adapt it in the future, while reducing the amount of global variable needed to achieve this.