The start directory of cmder is defined in that order:
1. The directory passed as parameter to the cmder executable
2. The `CMDER_START` environment variable
3. The `HOME` environment variable
4. The current user directory (`USERPROFILE` environment variable)
This commit also fix two issues:
* stating cmder with a path in parameter would set CMDER_START (whereas it may just be temporary)
* fix new line in cmd when starting cmder (this one was buggin me)
Existing code registered right-click only for blank areas of the
Explorer window. This change adds a menu item for right-clicking on a
folder in the file list.
Also adds the program's icon to help find it in a crowded context menu.
