IMPLEMENTATION

This file gives a general, possibly incomplete, overview of
the SacredBrowser implementation.

The SacredBrowser GUI is based on the PyQt4 bindings, so for in-depth
information, you may want to read general documentation about the Qt4 library 
and its Python bindings. SacredBrowser largely follows a class-based approach,
where classes are largely divided into model classes and GUI classes. The script
SacredBrowser.py starts the program.

Infrastructure and diverse classes
--------------------------
class Application:
    This is the main class within the PyQT framework. It creates a main window
    and takes care of connecting several Python signals and slots. It also maintains
    links to the current Mongo database and collection.

class Config:
    Intended to hold some global defaults. Don't bother.

class DbConnection:
    An interface to MongoDb.

Model classes:
--------------------------
class CollectionModel:
    This class represents a collection (i.e. actual database content). A representation is
    shown in the lower right of the SacredBrowser window. The class follows the Qt
    abstract collection model, which is complicated. 
    Note that there is one object of this class, which is reused when a different
    collection is to be displayed. (Otherwise the connection between the GUI widget
    CollectionView and this class would have to be broken and reestablished.)
    CollectionModel also saves some collection-specific settings, e.g. the displayed fields.

class DbModel:
    This class represents a model for the tree of databases, a representation is shown in
    the left part of  the SacredBrowser window. Follows the Qt abstract collection model.

Gui classes:
--------------------------
class MainWin:
    This class represents the main application window. It sets up the GUI, but has
    no further functionality.

class CollectionView:
    This class represents the main database display within the SacredBrowser window.
    It also has some functions to react to key and mouse events.

class DbTree:
    The database tree (left part of the main window). Note that all functionality is 
    contained in DbModel.

class FieldChoiceWidget:
    This class implements a widget consisting of two lists, one showing all available
    fields in the current database, the other one showing the fields which are 
    displayed (in order).

class FilterChoice:
    Text widget with some keys allowing to enter the desired filter for database
    entries. Also contains parsing logic (hmmmm...)

Gui classes:
--------------------------
class DetailsDialog:
    A dialog showing all details pertaining to an experiment (config settings
    and stored info in database).

class SortDialog:
    A dialog allowing to choose the sorting order for database entries.