add a constant given by RF as a configurable value under the name of 'Shunt Impedance'. Then allow it as a vble text name in the formula like the beam current. But in this case they write this value as implicit with calculations to do (2*3.3*1e6) an has to be evaluated.
add and eval to the facade formulas check to report syntax or other errors.

git-svn-id: svn+ssh://controls01/siciliarep/svn/trunk/tango_client/ctrflyrtech_fdl/trunk@13264 a18efa20-c439-0410-bf20-9b91ec695b4c
add the evalluation check to the Shunt Impedance

git-svn-id: svn+ssh://controls01/siciliarep/svn/trunk/tango_client/ctrflyrtech_fdl/trunk@13265 a18efa20-c439-0410-bf20-9b91ec695b4c