fix: Move ZclFrame.fromBuffer() out of adapter code

[Koenkk]

Move the ZclFrame.fromBuffer() out of adapter code to prepare for custom cluster definitions as discussed in #971

[Nerivec]

A few more suggestions...

• Moving this function to ZclHeader as write() (or something like that) for consistency. Also, frameControl doesn't need a variable in there, it can just be passed directly to buffalo.writeUInt8.

• Have something like this in ZclHeader:

    /** Returns the amount of bytes used by this header */
    get length(): number {
        return 3 + (this.manufacturerCode === null ? 0 : 2);
    }

    get isGlobal(): boolean {
        return this.frameControl.frameType === FrameType.GLOBAL;
    }

    get isSpecific(): boolean {
        return this.frameControl.frameType === FrameType.SPECIFIC;
    }

• In ZclFrame, this.Header.commandIdentifier is a duplicate of this.Command.ID. Also, frame.getCommand() seems to be called often enough just to get the ID (frame.getCommand().ID). Probably some optimizations needed around this.

[Koenkk]

All done! Let me know if this is OK now.

[Nerivec]

Looks good!