OpmFind.cmake: prevent multiple calls to the same module in the same run

this prevents to check for the same module more than once in the same
cmake run and should thus speed things up a bit as well as make the
output a bit cleaner. For this I assumed that the ${name}_FOUND cmake
variable does not get cached, which it seems like it does not...
cmake: make sure all calls to message() exhibit a type
OpmFind.cmake: also check for CAPITALIZED found variables

thanks to @rolk for catching this
Implementation (not finished) of wells_equal, well_controls_equal, and tests. To build a WellsManager test for old and new parser

Conflicts:
	CMakeLists_files.cmake
Added test_wellmanager which loads wellmanager from deck and tests many values.
Added test calls to wells_equal() and well_controls_equal().
Extracted everything related to well controls to separate header well_controls.h - to simplify introducing new parser.
Moved well_controls implementation to separate file well_controls.c.
Removed struct WellControlManagement and replaced with simple integer field cpty in the WellControls structure.
Removed #include <opm/core/well_controls.h> from wells.h and inserted explicit #include <opm/core/well_controls.h> where needed.
Added well_controls_get_xxx() and well_controls_set_xxx() functions. The well_controls_reserved() function is called from well_controls_add() and not explicitly.
Reimplemnted struct WellControls access to use the set/get functions in well_controls.c
Temporarily added symbol HAVE_WELLCONTROLS before including well_controls.h - to get acces to the internal elements in struct WellControls.
Using well_controls_get_num() and well_controls_get|set_current() in WellsManager
Changed test_wellsmanager to use well_controls_get_xxx() functions.
Changes test_wells to use well_controls_get_xxx() functions.
Added new functions to set target and type and invert value of current control.
Using new function well_controls_invert_current().
Added new function well_controls_iset_distr().
Implemented well_controls_add_new() with well_controls_iset_xxx() functions.