o.c.o.converter: improve handling of precision

in TextUpdate and TextEntry.
o.c.o.converter: Added ability to translate invisible shell command widgets
o.c.o.converter: Removed hard coded references to bright green

With EDM, the colours for alarm sensitive widgest are defined by the
forground/background colours.
o.c.o.converter: Rely on colors.list to define alarm colours in OpiWidgets

This assumes that the colours for alarms will be specified in the
colors.list file.
o.c.o.converter: Replicates EDMs behaviour for closed polylines
o.c.o.converter: Use non-alarm colours from EDM instead of the 'OK' green
o.c.o.converter: improvements to XY graph conversion

 * choose larger default buffer size (some waveforms with 4096 pts)
 * correct style and size for point graphs
Merge pull request #763 from dls-controls/converter

EDM to OPI Converter