Remove speed of light from input files.

Changing speed of light only makes sense in combination
with epsilon_0 and mu_0.
Modify particle streams by random components.

Streams can be modified by equally distributed random numbers in a range
(randomX, randomY, randomVx, randomVy)
or by Gaussian random distributions
(randomGaussX, -randomGaussY, -randomGaussVx, -randomGaussVy)
Add Weibel instability initial conditions as YAML file
Add initial conditions for "100 random particles" as YAML file
Merge pull request #91 from aipp/file

Weibel instability and random particles as YAML initial conditions