Add display_test and display_if functionality for fields

[mattblovell]

See the 21 Jan update to Idea #14.

TOML doesn't support the exact syntax shown in that post, but the general idea is certainly possible -- have a function to invoke and use the string returned by that function as a condition for rendering that fields entry.

[mattblovell]

I decide to make the TOML value a 2-element string array. Per a follow-up posting to Idea #14, the elements in the array are interpreted as follows:

• The first string must be either an available InfoLabel or a string callback function (i.e., an entry in the STRING_CB table).
• The second string is then compared against the result of "evaluating" the InfoLabel or executing the callback function.

When using display_if, the second string must equal the return value for the element to be displayed.

When using display_ifnot, the second string must not equal the return value for the element to be display.

This functionality is being rolled out for all fields array entries, as well as the top-level thumb and prog layout elements.

[mattblovell]

Some mostly non-sensical examples for setup.toml:

[A_LAYOUT.A_DEFAULT.thumb]   # Artwork
  posx = 3
  posy = 4
  size = 405
  # If artwork is smaller than the above size, should it be centered
  # where the fullsize artwork would have been placed?
  center_sm = 1
  display_ifnot = [ "test_track", "02" ]

[A_LAYOUT.A_DEFAULT.prog]    # Progress Bar
  posx   = 420     # upper-left corner x position
  posy   = 8       # upper-left corner y position
  height = 12      # pixel height
  short_len = 196  # length when elapsed time matches 00:00 (min, seconds)
  long_len  = 300  # length when elapsed time matches 00:00:00 (hrs, mins, seconds)
  color_fg = "color_7S"
  color_bg = "color_gray"
  display_ifnot = [ "test_track", "02" ]

[[A_LAYOUT.A_DEFAULT.fields]]
  name = "greeting"
  posx = 5
  posy = 0
  format_str = "Hello, Track 2!"
  display_if = [ "test_track", "02" ]
  font = "font_bold"
  fill = "white"

where the kodi_panel_demo.py script was augmented to contain:

def example_callback(info, screen_mode, layout_name):
    return info['MusicPlayer.TrackNumber']

kodi_panel_display.STRING_CB['test_track'] = example_callback

[nico1080]

works fine: eg in my setup: https://github.com/nico1080/kodi_panel/commit/60503a5faaba103dca5a401d68c5a4e7afe488b3