Sequencer cleanup with timing instrumentation

Contains the following changes:

• Sequencer is now fully configured via its Config object, including the number of events. The .run() functions takes no arguments anymore.
• Sequencer now has per-algorithm timing measurements. The timing information is written to disk in a tab-separated text file and also printed as a debug message. With the default log level only the total and per-event timing is printed to not clutter the output too much.
• The number of parallel jobs is now configured explicitly with the --jobs,-j command line flag. Support for reading the value from an environment variable (the name of which I could never remember) has been removed.
• Simplified options setup and parsing by moving boilerplate code into common functions.
• Include dfelibs as a submodule (used for writing timing information).

Requires !133 (merged) and needs to be merged afterwards.