examples: boris: first scaffold

not yet ment to work
tests: examples: boris: first tests

for particles and physics
examples: boris: enable in all examples
examples: boris: axpy for particle components (+tests)
examples: boris: remove axpy for particles; add convert

adding a convertion function to get from a velocity to a position and
from an acceleration to a velocity by multiplying a scalar time value

removing axpy for Particle as there is no need for adding to particles
(despite the question on how to actually do that)
examples: boris: using operator overloads for arithmetics

overloading =, *=, +=, *, + for particle components to reduce verbose
use of chained axpy-convert calls
tests: examples: adjusting particle tests
examples: boris: better using 3D, not 2D
examples: boris: first compiling version of Boris impl_solve
examples: boris: some boilerplate stuff

actually, I'v not the willpower to comment on this in detail
sweeper: make that thing protective, not private
examples: boris: no shrd_ptr inside of particles

this ease overriding operators and enables C++11's move semantics
cmake: better error output with Clang
examples: boris: a few tweaks and fixes
examples: boris: implement simple E-/B-fields
examples: boris: further progressing to completion
examples: boris: fixing particles
examples: boris: fixing physics
examples: boris: it works! (almost :-/)

for M=2 and one single SDC iteration (plus predict)
examples: boris: finally, it works

also for M>2