unified script versions

All scripts have the same version which is set in single file (VERSION).
All setup.py and conf.py scripts containing these version numbers were
renamed to *.skel. These skeletons are then read by makefiles and proper
*.py scripts are generated out of them.
updated README
updated make_new.py scripts
updated commands readme
propagate usage strings to subclasses

When usage string is defined for some parent class of some command
without any usage, it will now be inherited from parent.
turned few error messages into sentences
added session proxy

Allow to override session object for some command and all its children.
Proxy encapsulates main session object and provides limited access to
its uris and connections.
added suppport for profile and class requirements

Added special command LmiSelectCommand taking set of conditions with
associated commands to load. Conditions must be met for command to be
loaded. They contain profile and class requirements on remote broker.
fixed creation of command with helpers

Module name of commands created with helper functions
(register_subcommands, make_list_command) was taken from one of base
classes which is wrong. It should have the name of module where it's
defined.
added select_command helper

It is a function that builds LmiSelectCommand subclass.
updated doc for version requirement specification