improve load time when there are many files to open

[szabgab]

When there are many files to open at launch time of Padre it takes a lot of time.
 http://www.nntp.perl.org/group/perl.wxperl.users/2008/11/msg6247.html

Based on the idea of bricas we should try to only create the notebook with the necessary tabs showing the file names but create the Editor object and load only the file that is actually gets the focus.

Later either load the rest of the files in the background or load them only when they get focus or otherwise are needed. (eg. a search through the files.)

[adamk]

Padre is really quick now opening lots of files, marking as fixed.