Allow loading of multiple files in mipsy_web

[Dylan-Brotherston]

Most file picker dialog boxes allow for multiple ordered files to be selected. This feature in mipsy_web would allow multi-file projects to be ran, like mipsy_cli does.

[spanishpear]

This is also pretty difficult - I forgot multi-file projects even exist in mips... this is a stretch feature currently any thoughts for what the UI might look like?

Was thinking to just concat the files in with a hide/show to collapse individual files - and then from my memory of how multifile projects work - should disasseble to the same binary anyways so that should be fine...