Upload file unification

[tomusdrw]

We currently support uploading a file in two places:

1. JSON
2. Bytecode.

Instead, there should only be one option to upload a file and we should auto-detect if it's a JSON test file or PVM program (decodeStandardProgram).

The file should also be validated before being imported:

1. If we detect JSON, but it does not have all required fields - we should given an error about invalid JSON file.
2. If we detect binary, but it can't be decoded - we should display error that occured during decoding.

Over time uploading binary files will be much more common so it should be a more streamlined input method.

[tomusdrw]

Jam Service (1).pvm.zip

Here is a file in the SPI format (coming from paritytech/polkavm#190) that can be loaded now in the debugger (using RAW Bytecode tab).

However it seems that from the SPI we only use the raw program code and we don't use it to initialize the memory.

The file should most likely be just passed directly to resetJAM function of a PVM: #132 and we should let the PVM initialize itself.