Allow swagger to be excluded from build

[eternal-flame-AD]

I discovered that swagger UI is heavy in the final binary. I tried building without it and got the following results:

Swagger + WebUI	Swagger Only	WebUI Only	No User Interface
39M	33M (-17.9%)	28M (-28.2%)	21M(-46.1%)

I think most people would not use the Swagger UI functionality, and a nearly 30% decrease in binary size is worth doing from my point of view, this is substantial if it is running on a highly limited environment(like an OpenWrt router, etc.).

Changes Proposed

1. Add two build tags(nowebui noswagger) to exclude Swagger UI and WebUI from builds.
2. Permit CORS to /swagger and redirect /docs/*any to the swagger UI hosted on gotify.net page with our custom URL to /swagger.

Example: eternal-flame-AD@47a37cd

[jmattheis]

Good Catch.

I don't really like having multiple binaries with different features. I'd say we only have one optimized binary.

Currently a full swagger ui is shipped with gotify/server, we could only ship a html file with external dependencies like this: https://github.com/gotify/server/blob/0a32e86bcac4bc5471887dc0580a3b9442a5ebe1/docs/ui.go
This reduces the size of the swagger ui to 1.63KB.

Futhermore images could be optimized by https://imgbot.net/ see #115 (optimized less than I expected (: )

And lastly we can use the linker flags -w and -s which both strip debugging information.

[eternal-flame-AD]

If you don't want to make any compromise on features, upx can compress the binary by around 50%

[jmattheis]

upx seems pretty amazing, it shrinked my binary to 6MB.

[eternal-flame-AD]

That is impressive. Maybe we can consider adding upx into release workflow.

[jmattheis]

For adding upx I've created #118. The rest should be fixed with #116.