Updated order of carrying out operations in readSlipPlane function.
The operations of reading in data are carried out in the following
order:
-Extremities are read in and stored in SlipPlane::extremities.
-Dislocations are read in one by one, and inserted into the std::vector
dislocations.
-Dislocation sources are read in one by one and stored in the
std::vector dislocationSources.
-The two vectors are sorted in ascending order of distance from
SlipPlane::extremity[0].
-The std::vector defects is updated using the function updateDefects:
--The extremities are assigned to the ends of the vector.
--The dislocation list is inserted.
--The dislocationSources list is inserted.
--The defects are all sorted.

Henceforth, care must be taken to call sortDislocations and
sortDislocationSources functions every time a new dislocation or a new
dislocation source is inserted or removed. The updateDefects function
must then be called to update the defects list.