Changing data connection parameters from hardcoded values to configurable values.

The server now attempts to read, currently depending on OS platform, the following values:
on Windows:
Connection/Port

i.e. looking for this config part:
[Connection]
Port=portnumber

Default for portnumber is the previously used 4444.
Since QTcpServer allows special value "0" for "any available" socket, it might be a better default.

on Non-Windows:
Connection/SocketDirectory

i.e. looking for this config part:
[Connection]
SocketDirectory=rel_to_home_or_abs_path

Default path is ".akonadi", i.e. $HOME/.akonadi
A starting KDE session should probably set this to the user's KDE socket directory if not explicitly set to something else.

After creating the respective server socket, the server will create a config file named akonadiconnectionrc, containing the actually used parameters.

On Windows it will basically look like this:

[Data]
Method=TCP
Address=127.0.0.1
Port=4444

On Non-Windows it will basically look like this:

[Data]
Method=UnixPath
UnixPath=/home/username/.akonadi/akonadiserver.socket

Additonally the server will add the address of its D-Bus session bus to the config:

[DBUS]
Address=unix:abstract=/tmp/dbus-IvFq3ku5bA,guid=23b1bbaca93a129ad21fcb0046c6e1db

This is currently not used on the client side, but would eventually allow clients with a different session bus.