Sort out if machine is a needed argument to tool base class init

[brendenpelkie]

Tool base class takes a machine but this doesn't seem to be needed. Is it? I took it out while debugging and never looked into if that will break something or not. I think there was some issue on instantiation of a tool if machine attribute was not defined in base class instantiation.

[bsubbaraman]

It shouldn't be needed; instead, the _machine attribute is set in load_tool(). Anecdotally I've been using the repo for a while without passing the machine explicitly and hadn't run into any errors.

I did notice that the Pipette module takes a machine instance as a parameter, which I think is redundant/not necessary.

[MariaPoliti]

I've removed the redundant attribute _machine from the Pipette and WebCamera tools. I've kept it in the base Tool class, but I am happy to remove it if it is considered uneccessary.