Implement a session logging feature

[walterpg]

Several bug reports include a dialog screenshot or a text description of a one-line error message. Most of these are helpful to neither users nor the developer.

The proposed enhancement is an optional plugin session logging feature. Most "one-liner" messages are the result of an unforeseen condition or exception for which more detail is available that could aid users and bug fixers. Logging might also provide a record of successful operations performed by the plugin.

While plugin's existing user feedback mechanisms (dialog, status) could be used instead of a background logger, details such as call stacks and inner exceptions usually exceed the limits of general UI and user's patience.

The logging feature could be added as a new tab on the existing Configuration dialog, or as a standalone dialog. Any log text UI should be backed up by a single, overwrite-able file. Instructions for submitting bug reports should be updated to request that users attach the session log file when needed.

[walterpg]

Partially implemented in the current release