task-base: major restructure

task-base: major restructure
- task-base-FEATURENAME are built nevermind does MACHINE supports them
- task-base depends on task-* packages only - MACHINE/DISTRO features only
- task-boot contain stuff needed to get minimal bootable image
- task-distro-base contain distro addons
- task-machine-base contain machine specific addons
- ability to choose SSH daemon (dropbear, openssh, none) by distro
- ability to choose /dev/ manager (udev, devfsd, mdev) by distro
- ability to choose getty provider (tinylogin by default) by distro
With this version it is easier to create smaller rootfs - for example
image with ONLY bluetooth support is "task-boot + task-base-bluetooth".