Electoral district filtering

[dtinth]

[0pdd]

@dtinth 4 puzzles #19, #20, #21, #22 are still not solved.

[0pdd]

@dtinth 3 puzzles #19, #20, #21 are still not solved; solved: #22.

[0pdd]

@dtinth 2 puzzles #19, #20 are still not solved; solved: #21, #22.

[0pdd]

@dtinth all 4 puzzles are solved here: #19, #20, #21, #22.

[rapee]

Close due to ชนะถล่มทลาย and ชนะฉิวเฉียด has its own issue on #104, #105