Feat/add symbol opacity

[bordoray]

Issue

close #94

変更内容:Description

• タイトルのとおり

テスト手順:Test

Test on symbols with opacity.

Symbol opacity parameter can be show as follow:

• For point layer, click on "Marker" as below
• For Line layer, click on "Line"
• For Polygon, click on "Fill"

Expected result for 50% opacity

その他:Notes

• 特になし

[bordoray]

↑ How is this ?