Merge base libraries into a single library

This patch simplifies the way of how Genode's base libraries are
organized. Originally, the base API was implemented in the form of many
small libraries such as 'thread', 'env', 'server', etc. Most of them
used to consist of only a small number of files. Because those libraries
are incorporated in any build, the checking of their inter-dependencies
made the build process more verbose than desired. Also, the number of
libraries and their roles (core only, non-core only, shared by both core
and non-core) were not easy to capture.

Hereby, the base libraries have been reduced to the following few
libraries:

- startup.mk contains the startup code for normal Genode processes.
  On some platform, core is able to use the library as well.
- base-common.mk contains the parts of the base library that are
  identical by core and non-core processes.
- base.mk contains the complete base API implementation for non-core
  processes

Consequently, the 'LIBS' declaration in 'target.mk' files becomes
simpler as well. In the most simple case, only the 'base' library must
be mentioned.

Fixes #18
Update example configurations

With the change of the Timer::Session interface, all scenarios that use
the timer use core's SIGNAL service. So we need to route sessions
accordingly.

In addition to the adaptation to the changed timer, this patch removes
some stale examples that predate the run tool and are no longer used.
base-hw: fix bug in 'Platform_thread::pager()'
base-hw & arm_v7: fix CPU initialization bug

ref #601
hw_arndale: create builddir support

ref #601
arndale: UART driver base

ref #601
arndale: board driver base

ref #601
cortex_a15: base/mk spec

ref #601
arndale: base/mk platform spec

ref #601
hw_arndale: enable nested init test

fix #601
base-hw: rework 'run/env', enable '--target uboot'

ref #601
ref #598
base-hw: provide SIGNAL service in nested_init.run

ref #601
base: make signal framework usable for base-hw

ref #641
base-hw: destroy signal contexts, generic signal.h

fix #641
timer & hw & omap4: compile bug in Platform_timer

fix #652
base-hw: useless default assignment in syscalls.h

fix #588
base-hw & arm: bugs when zero-filling BSS

fix #654
base-hw: rebase onto base lib merge of @nfeske

fix #18