Small updates to logging in package manager

The package manager no longer logs to the .dtflog file. Maybe
someday we'll add a command-line argument to allow this.  The
"pydtf" logging functionality has been modified to account for this,
which involves lazy-loading the .dtfini file.
Added component listing and checking for components

Modifications to "dtf_core.sh" to allow shell modules to determine
if a component (module, binary, library, package) is installed.
Added functionality to dtf_package_manager.py to list installed
components with the "dtf pm list" subcommand.