Prevent unnecessary compilation

[rose-m]

When the assets compiler is started, it will compile all code for any plugin inside the required dependency chain.

However, if the assets compiler is started twice in direct succession without any modifications to the code, then there would be no need to do the compilation again (exception: the --clean flag is specified).

Goal: Prevent unnecessary asset compilation by computing a unique hash on the file content(?) and save the last compiled hash.

[rose-m]

This can be regarded as closed by the introduction of TypeScript 3.4 in the cplace repository which now has incremental compilation.