ENH: Added logging functions for Python

Added info and error logging macros for Python modules.

Usage examples:

```
import slicer.log

slicer.log.info("This is an info message, logged as an INFO type message")
slicer.log.info("This is an info message, logged and also displayed in a popup for a short time", True)
slicer.log.info("This is an info message, logged and also displayed in a popup for 5 seconds", True, 5000)
slicer.log.info("This is an info message, logged and also displayed in a popup, the user has to click OK to continue", True, 0)

slicer.log.error("This is an error message, logged as an ERROR type message")
slicer.log.error("This is an error message, logged and also displayed in a popup, the user has to click OK to continue", True, 0)
```

From: Jean-Christophe Fillion-Robin <jchris.fillionr@kitware.com>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23818 3bd1e089-480b-0410-8dfb-8563597acbee
ENH: Update scripted module base class to leverage "slicer.log" functionality

From: Andras Lasso <lasso@cs.queensu.ca>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23819 3bd1e089-480b-0410-8dfb-8563597acbee
ENH: Improve scripted module templates

* Use "slicer.log" functionality

* Also update the scripted loadable module template to perform actual
image processing (thresholding, using a CLI) and not just
capture a screenshot, because this is much closer to what
most users would do.

From: Andras Lasso <lasso@cs.queensu.ca>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23820 3bd1e089-480b-0410-8dfb-8563597acbee