This commit is the second of an incremental serie. There will be other
commits with the information about tasks and the support for BSD and
Solaris once things are settled.
The TaskManager class is build with a new source task-manager-linux.c
that provides functions specific to the Linux implementation. It has
functions to read the usage of the memory/swap and the CPU.
Added the TaskManager class to hold system information and tasks.
Currently it provides username and hostname based on POSIX functions.
The Swap is now part of the system information and is being displayed in
the statusbar.
