fixes for warnings/errors with Xcode 10.2

See merge request !61

Cof

Closes #282

See merge request !60

improve starting radial guess as suggested in Gordon's paper, but pr did not improve in the PSI Ring case, for #282

fixing orientation of dipoles in *_ElementPositions.txt and starting and end points of elements where the edge doesn't coinside with beginning

Resolve "Specify trim coil range azimuthally"

Closes #276

See merge request !53

This reverts commit 5fbd4c4b.

Switch 'ENABLE_OPAL_FEL' added to enable OPAL FEL. OPAL FEL requires
MITHRA. MITHRA will be searched for in the usual directories and paths.

Master

See merge request !59