#10 Add a timestamp to the status line header

[Mirko Raner]

Currently, ebuilder only prepends the [ebuilder] header to each output line. It would be helpful if that header also included a timestamp, counting from the start of the build, e.g. [ebuilder 05:39]. Additionally, it might make sense to print an extra empty line with a header if no console output was received for a certain time (e.g., for a minute). This can help identify stuck builds, which is difficult right now unless someone is watching the build the whole time.
This feature probably requires a refactoring of the console logging code, which right now sends an [ebuilder] string to the console in various different code locations.