Embed swagger UI

[caco3]

This PR embeds the Swagger UI into the Web Interface. To keep the additionally required flash usage low, most files get pulled from a CDN.

I also renamed the last tab Forum to Help and extended the tab with a section for the REST API documentation.
The great advantage for an embedded Swagger UI is to be able to directly send the cmds to the device.

Updated UI

Swagger UI

Direct calls to the device

[tueddy]

Just tested, works fine!

[tueddy]

@caco3 Looks good so far!
One issue i found, Web.cpp is getting recompiled even nothing has changed:

Building in release mode
Compiling .pio\build\lolin_d32_pro_sdmmc_pe\src\Web.cpp.o
Linking .pio\build\lolin_d32_pro_sdmmc_pe\firmware.elf

We had this before and #293 fixed the issue.
Maybe same here?

[caco3]

Good point, I changed it to make sure the mtime does not change.

BTW, this PR adds 3544 bytes to the flash usage. If this is a problem, we could create a define in settings.h so it could be added optionally. The static RAM usage is unchanged although we added 3 extra files to the webserver.

[tueddy]

Tested against Lolin D32 (without PSRAM) & additional flash usage is OK