WIP: Implementing EvToolbar as an abstract base class, which EvRecentViewToolbar
and EvMainToolbar can inherit
WIP: Implementing the abstraction, yet
EvRecentView: Almost finished abstraction of the toolbar

Now there is a EvMainToolbar, EvRecentViewToolbar, and EvToolbar. Just need
to check that everything is done correctly.
EvRecentView: Renamed list_store to model
EvRecentView: Changed all uses of 'self' to 'ev_recent_view'
EvRecentView: Used signal_id for disconnecting, instead of disconnect_by_func
EvRecentView: Replaced gpointer with EvRecentView * in the parameter

Using EvRecentView * rather than gpointer user_data in callbacks for
button-release and button-press
EvRecentView: Fixed the way I was getting the EvDocument from an EvJobLoad

I was accessing the data structure directly. On KaL's suggestion, I used the type
conversion to the parent and then accessed the EvDocument.
EvRecentView: Fixed style problem in code.

Specifically, line between decalaration block and code
EvWindow: Removed return statements at end of void functions
EvWindow: Fixed style problem in placement of curly brackets after if statement
EvWindow: 'items' -> 'documents' in button name and description
EvWindow: Removed a stray extra line
EvRecentView: Removed use of unnecessary GD_MAIN_COLUMN_ID
EvRecentView: Removed unnecessary start of signal id from 1
EvRecentView: Fixed style irregularities in function headers
EvRecentView: Fixed style irregularities in declaration blocks
EvRecentView: Use NUM_COLUMNS instead of 11
EvRecentView: Shortened the code in ev_recent_view_new
EvRecentView: Refactored the button press and release callback handlers

There were a number of recommendations which KaL had made in his review. I
have made these changes based on them. It basically removes unnecessary use
of labels and string functions.