dg1d: Add limiters.jl

• Collect most of the limiter implementations into limiters.jl (there still remain bits in ScalarEq)
• Add new limiter limit_slope_preserve_continuity! that is tailored towards the Bspline approximation (although its not working well)
• Add new limiter limit_slope_convex_hull! that is tailored towards the Bspline approximation
• Add new reftests burgers_sine_bspline1_limit_slope_convex_hull and ``burgers_sine_bspline2_limit_slope_convex_hull`
• Fix Bspline integration

added 1d bugfix feature new reftests refactor labels

enabled an automatic merge when the pipeline for 89f1c1d5 succeeds

aborted the automatic merge because source branch was updated

added 5 commits

• 5189e2e9 - add reftest burgers_sine_bspline1_limit_slope_convex_hull
• 9d1d4c0d - apply limiter to modal values
• 5de4bf7c - add reftest burgers_sine_bspline2_limit_slope_convex_hull
• f3b49dcf - update testconfig
• 6bbc7963 - rename a limiter

Compare with previous version

merged

mentioned in commit eeaf318b