Fixed a bug with DHCP proxy mode, created separate LICENSE.md, minor improvements to README.md

Bug Fix
----------
**Problem**
If ```--no-dhcp``` is specified as an argument the DHCP server still starts because ```--proxydhcp``` default is True and that argument sets ```DHCP_PROXYDHCP``` to True which, in turn, effectively overrides the ```--no-dhcp``` argument and starts the DHCP server.

**Resolution**
Changed the default of ```--proxydhcp``` to False so that if ```--proxydhcp``` is specified as an argument then it becomes True and the DHCP server is started in proxy mode. Not specifying ```--proxydhcp``` means that the DHCP server will not be started in proxy mode (either by specifying the ```--dhcp``` argument or by _not_ specifying the ```--no-dhcp``` argument).

Other Improvements
---------------------------
Added some level of verbosity when each service is started and when PyPXE as a whole has finished initializing as well as when PyPXE stops (via keyboard interrupt).

Implemented try/except in ```__main__```

Added minor comments throughout to help understand what’s going on

Removed license from README.md and created a separate LICENSE.md

Updated README.md to reflect minor change in ```--proxydhcp``` argument help statement