base-linux: revised region management

Revised region management detects region conflicts by using _soft_
mappings per default. Overmapping is activated for population of managed
dataspaces only. For more information see header documentation of
base-linux/src/base/env/rm_session_mmap.cc.

Related to #883.
Move main bootstrap to platform-specific object

To prevent multiple execution of main-bootstrap, I moved the code to a
statically initialized object. The reason for this change is that
_main() is exeuted twice when starting dynamic binaries. Now, the object
is part of the base-common library which is linked with ld.lib.so.

Also fixes #883.
Increase quota of lwip_lx.run

See 33909779 for documentation.