[mhwd-kernel] add rt-kernel support and some small modifications

I've tested this thorrowly running different kernels and all possible scenarios I could think of and everything seems to work fine.

kernel_repo()

kernel_list()

Some stuff is even a little fancier now

The only little flaw is that when rt switches to a different basekernel this has to be adjusted manually until someone comes up with a more brilliant solution than this:

rt_base=linux46
rt_lts_base=linux44

IFS=. read -r major minor _ <<< "$(uname -r)"
current="linux$major$minor"
[[ $(uname -r) == *rt* ]] && [[ $current == $rt_base ]] && current=linux-rt-manjaro
[[ $(uname -r) == *rt* ]] && [[ $current == $rt_lts_base ]] && current=linux-rt-lts-manjaro

Created by: philmmanjaro

At the current state we have to update mhwd-kernel whenever you change the base of your RT kernels. Maybe you should ship a file in a package called mhwd-rt which is optional to support RT kernels. It has a simple config file we read out and only that package needs to be changed. Like we do with mhwd-nvidia and so on.

I think we can even collect the necessary information from what we have already installed... I'll come up with something!

I think I found something. Have a look!