allow flatshape (command line syntax) theming

[fdncred]

This pr allows one to specify alternate colors for the flat shapes that are used in the cli command line.

I also separate out the config into a nu-color-config crate so that it could be used in multiple places without having circular references. I ran into some issues implementing this that pushed me to move it into its own crate.

I also ran into a problem where versions of nu-ansi-term were conflicting with each other and/or reedline's version. To combat that, I commented out all of them pointing to ../nu-ansi-term and just pointed them to the crates.io version. I'd like to fix this but I'm not sure how.

example color_config with the "red" theme.

let config = {
  color_config: {
    separator: $base03
    leading_trailing_space_bg: $base04
    header: $base0b
    date: $base0e
    filesize: $base0d
    row_index: $base0c
    bool: $base08
    int: $base0b
    duration: $base08
    range: $base08
    float: $base08
    string: $base04
    nothing: $base08
    binary: $base08
    cellpath: $base08

    # below are the cli syntax colors
    flatshape_garbage: red
    flatshape_bool: red
    flatshape_int: red
    flatshape_float: red
    flatshape_range: red
    flatshape_internalcall: red
    flatshape_external: red
    flatshape_externalarg: red
    flatshape_literal: red
    flatshape_operator: red
    flatshape_signature: red
    flatshape_string: red
    flatshape_filepath: red
    flatshape_globpattern: red
    flatshape_variable: red
    flatshape_flag: red
    flatshape_custom: red
  }
}