Extract color calculation from column_line_print

Into prepare_primary_col_color() and prepare_secondary_col_color()
functions.
Prepare ui.c unit for 'number' option
Recalculate real number width on draw operations
Consider numbers column on drawing file list
Draw line numbers in file list
Add 'number' option
Add 'numberwidth' option
Store new options in vifminfo
Highlight new options in vim
Update one of TODO's in engine/options.c
Merge branch 'add-file-numbers'

Add 'number' and 'numberwidth' options to control displaying of file
numbers.

Thanks to filterfalse and greye.