[!!!][TASK] Rewrite install tool

Main features:
* The god class "Installer" is gone and split into two major parts.
A step controller handling major upgrade and install tasks, and a
tool controller handling the known install tool actions.

* The step controller is designed to be always called prior to the
tool controller, if a step needs execution, it comes up, otherwise
the tool controller will be executed.

* The entry point typo3/install/index.php is gone and substituted
by typo3/sysext/install/Start/Install.php. The file contains a
lengthy comment to document the main request flow and used GET/POST
parameters.

* Most parts of the install tool do not bootstrap the whole system
anymore, in general only the base bootstrap, dbal (if loaded),
extbase and fluid ext_localconf.php are loaded. This makes sure
the install tool can not fatal if some extensions ext_localconf
is broken. The whole install tool runs without any caching, so a fatal
in some cache file can not kill the install tool execution.

* Insta...