feat: support for WASM

[wdconinc]

This PR enables a WASM build of JANA2. This consists of a few categories of changes:

• new CI to deploy a WASM build to GitHub Pages with emscripten, and a web interface to run JTest,
• changes to the CMAKE_INSTALL_*DIRs (submitted as feat: use CMake's GNUInstallDir #518),
• changes to the typing for 32-bit WASM (submitted as fix: explicitly static_cast event number from uint64_t to size_t #519),
• dedicated WASM bypass code to handle files produced by the JBenchmarker,
• dedicated WASM bypass code to disable JBacktrace functionality,
• bypasses of pthread calls when using emscripten.

Draft until #518 and #519, and then I'll rebase.