Source directory restructuring

[Geert Janssens]

So after my houskeeping message in which I have announced the changes to src/
business and src/libqof, I'd like to bring up my eventual goal for the source 
tree.

My main motivation to do all this restructuring is to simplify. There are 
currently plenty of directories and I often have to guess where to expect a 
file. The qof vs engine story was one example. Is gnc-date something for qof 
or for engine ? I find myself regularly searching for a file in the wrong 
directory.

So here follows a first proposal for the directory structure I'm targetting:

* data (for things like art, checks, account hierarchy templates,...)
* doc (for all documenation)
* lib (for all source required to build "libgnucash", see below)
* ui (for all the user interfaces the project currently supports)

I am omitting some smaller directories here, such as util and macros. They 
will probably stay on the current top level for now.

I'm envisioning "libgnucash" as the core library that encapsulates all gnucash 
related concepts (the accounting concepts such as transaction, split, as well 
as the data backends). This library is what all applications in the gnucash 
sphere should depend on to implement the "gnucash" experience. The most 
obvious is of course the current gnucash as we know it. However at some point 
this library should ideally also become the core of the Android app and *who 
knows* one day an IOS app. And closer to the current state, it should also be 
the library that the guile and python bindings depend on. So all functionality 
encapsulated in one single library, the API. In practice I think the following 
directories belong in this libgnucash: core-utils, gnc-module, engine, the 
backends, app-utils. (Note I would like to get rid of gnc-module still, but 
that's a whole other discussion and task).

The ui directory will have a subdirectory for each user interface we support. 
This is not necessarily a *graphical* user interface though. At this point 
there are already a number of them:
gnucash
cutecash
bindings (with subdirectories for python and guile)

The bulk of the other directories are support directories for one of the ui's 
and I propose to make them subdirectories of each respective ui.

For example gtkmm is only used by cutecash, so let's store it there (until 
another ui would also require it, which I consider unlikely to happen still).

The other directories (gnome-utils, gnome-search, gnome, register, html, 
report, import-export,...) are all used only in the gnucash application and 
hence should be moved there. In the move I'd like to try and reduce the 3 
gnome* directories to one and call it gtk as we're not using any gnome 
specific technology any more.

In a later phase I think it would be nice if the core libgnucash could also 
spit out html reports, but that would require us to refactor the report 
modules, which I consider too much work to be done at the same time. When this 
eventually gets done the non-ui part of the report system can then be added in 
libgnucash to the benefit of all consumers (gnucash/cutecash/Gnc4Android/...).

Feedback or questions ?

Geert