Replace SEVERITY_ERROR by RPT_SEVERITY_ERROR to avoid collision with a system definition.
Replace other SEVERITY_XXX by RPT_SEVERITY_XX for consistency.
Fix compil warnings and some other compil issues.
There are lot of places where constants are used in the KiCad UI
as "magic numbers". The most common one is "5", used in many
wxFormBuilder and manual UI constructions as the margin.
This commit provides a place for all UI to look up shared
constants and other functions, to help create a consistent UI using
functions that provide meaning and intent to these magic numbers.