Add generic concept to colorize items in arb

[westram]

All items (genes,species,…) should allow to be displayed in any color in the various display clients (-display, editor, gene-map, ..).

Needs #682

The used color should be determined on the fly from item-data, e.g.

1. from the database field ARB_color (which provides the current coloring mechanism),
   usage of color-groups and coloring of marked items can be toggled in shader-setup-window
2. from a database field containing some numeric value for 1-3 -fields with [15001]
3. from an ACI expression transforming custom item data into a numeric value with [15035]

Case 1. directly provides a GC (status quo).
Cases 2. and 3. provide a value which will be mapped to a color-range (e.g. value=[0..100] ⇒ color[yellow..red]).

Additional features/settings (for cases 2. and 3.):

• define how color-range shall be mapped to value-range with [15015]
  • once (simple, but expressive)
  • multiple times (repeated forward mapping or interleaved forward/backward mapping)
    • allow fractions for mapping factor, add scaler to GUI
• value-range with [14997]
  • allow to specify using min/max input fields (+scalers)
  • add a range auto-detection
• values outside the value-range could be
  • mapped into the range (first/last color) or
  • skipped (=drawn in default GC)
• allow to store/restore the active color-customization in configurations with [15042]

Note:

• each itemtype needs its own config window
  no. each canvas(-type) has its own config window

Use case:

• colorize species according to their position in a given topology (see #444)
  [implemented dynamically]

[westram]

obsoletes #308 and #309