[IZPACK-1095]

This is to address http://jira.codehaus.org/browse/IZPACK-1095

1. TargetConsolePanel does not show/remember user's most recent installation path.
- Fix by synchronizing the getPath() method from TargetPanelHelper
- Always check for install path from your InstallData before trying to retrieve a default target path

2. TargetConsolePanel does not check if path is writable.
- Fix by synchronizing the isWritable() method into PathInputBase
- Had difficulty figuring out a way to synchronize validation methods since we don't have mixins/traits let me know if there is a better solution

3. Path normalization for TargetConsolePanel is out of sync with functionality in TargetPanel. For example the tilde is not expanded to the the user's home directory on Unix systems.
- Fix by synchronizing a normalizePath() method into PathInputBase

4. Installer fails when installation path is defined to a file.For example /home/user/example_file
- Fix by checking if path is a file within TargetPanel and TargetConsolePanel