Adding control for the sources list file for apt-get
Added check for running apt-get on only the following conditions (any met): there is no apt-get update cache data (eg. first run) OR any file in the /etc/apt/** was changed after the last execution OR it was executed more than 24h ago
Whitespace fix (from tabs to spaces)
Splitted the base packages installation into two types: essential (packages present in every instance) and shared optional (packages that work as base for another packages but dont need to be installed right away. Eg. Java). The last on is a virtual package declaration and needs to be resolved into the classes that use it