MFH: r504995

deskutils/conkyemail: Fix invocation of Python script at runtime

Since the default version of Python has been switched to 3.6 in r498529 the
script "conkyEmail.py" that is invoked by the shell script "conkyEmail"
fails at runtime due incompatible code.

This occurs only if the Python meta port is also installed otherwise it
won't start at all due a hardcoded reference (= /usr/bin/env python) in the
shell script, thus:

• Update and simplify the patch for "conkyEmail" by using placeholders for the Python interpreter and ${DATADIR} that will be replaced by the post-patch target. [1]

Also while I'm here:

• Silence all commands of the post-patch target to reduce cluttering of logfiles
• Add license information
• Pet portlint

PR: 238487
Submitted by: Katsuyuki Miyoshi <katsubsd@gmail.com> (initial patch)
Approved by: ports-secteam (blanket: runtime fix, framework compliance)