improve: export raster image as rendered image

[Kanahiro]

Issue

close #81

変更内容:Description

• I've realized it is possible to use same logic for exporting any type of raster layer and integrated each logics for file and wms.

テスト手順:Test

• Check exporting raster layer file-based and tile-based

その他:Notes

• 特になし

[Kanahiro]

this is not good because outside of original image is filled by white color:

I'll fix this

[bordoray]

layers has no crs (it looks well placed though)

For file raster, white background is remaining idk if it is fixed or not yet however

[Kanahiro]

Can I get the raster you tested?

[Kanahiro]

looks good even when your tiff: no-data in tiff is transparent in PNG

[Kanahiro]

[Kanahiro]

raster layer which has opacity looks not good...

[Kanahiro]

@bordoray made some changes:

• improve output layer which has opacity
• skip output if layer is empty (to catch this, added and renewedresult from process method)
• don't output in project.json if it is skipped

[bordoray]

Opacity looks good!

raster still have no CRS though.

[Kanahiro]

raster still have no CRS though.

it is not problem because

• world file is used only for checking
• raster image with world file has no crs (it is natural)