[devmgr] Sets default PATH when launching programs

Sets default PATH to `/system/apps:/system/bin:/boot/bin` when launching
a program.

US-259 #done

Change-Id: I62308699d66607e79a2c1cbe9476d8ed92e59cda

[dash] Integrate with linenoise

Dash now uses linenoise for line editing, including history. This patch
also removes the built-in history system, which requires libedit and
which we were not building.

Change-Id: I6d9837f34b12681618c4bce3d80bec7b8180bb74

[dash] Import dash 0.5.9.1

This is dash at revision afe0e0152e4dc12d84be3c02d6d62b0456d68580 from
http://git.kernel.org/cgit/utils/dash/dash.git/

Change-Id: I640f85e59520531ad7c65b7b35f00651e5cbc5d9