tbtool: Support installing apt dependencies in the tingapp bundle

[joerick]

Some tingbot apps will require system-level software to be installed, via apt or dpkg. While it's possible to write this into the program itself, it would be neater to design a declarative format (similar to requirements.txt) for this purpose.

Design goals

• Simple to write
• Declarative format - it should be possible to quickly check for the presence of packages on the system, to avoid a slow apt-get update call on app launch

[njh]

My bbcradio tingbot app uses mpg123. Would be great to be able to specify this as a dependency.

It also requires some re-configuration to make it play out of USB speakers.
Might be better to detect or provide an user-option to choose an output device, but wanted to avoid making the code too complex.

[furbrain]

also, my DNLA player/browser/controller will use mplayer - would be nice to have a neat way to install this.