Improved autoselection of method

In this patch I have done two things and it is possible to omit any one of the.

- Enable autoselection of the DRM method if neither RandR or VidMode is available.

- Check environment variables if it is safe to use the method despite not being flagged for it.
  DRM will be used if running in neither of X and Wayland (I do not know how to check Mir
  so you have not added that,) the patterns of the values in the environment variables are not
  sanity checked only existance and non-emptyness is checked. Similarly RandR and VidMode
  check if running in X, however because both are flagged for autostart, neither will actually do
  this check.

There is also a third commit that removes the first commit, it entirely removes the autostart
flag and forces use of the adjustments methods' functions to check whether they can autostart.