convert seismic data reader and writer into standalone tools

[rmodrak]

Currently, routines for reading and writing seismic traces are tied to individual solver repositories. Converting them to standalone tools would reduce dependencies between classes and make for a much simpler import system. Before proceeding though, we would need to be sure that our ability to (1) parallelize data processing operations and (2) handle multicomponent data would not be adversely affected.

[rmodrak]

This issue should be considered concurrently with Issue #6 "use obspy input/ouput and signal processing tools where it makes sense".

[rmodrak]

This item has been completed: the seismic reader and writer have been decoupled from the solver interfaces. In their place, reader and writer modules have been added to seistools. The import system has been greatly simplified.