[CPP-78][CPP-79]Navbar + TCP / File comms, disconnect, pause

[john-michaelburke]

Backend

• Merged TCP connection, File connection, (soon) serial connection, pause, and disconnect into a generic "ConnectRequest" capnproto.
• Moved TCP/File/(soon) Serial requests to a ServerState struct with associated functions for easier handling of the threads they run on.
• Attempted to clean up the footprint of client_send clones by pushing it through the MainTab struct which passes it down to all subtabs. (My implementation has way too many statics so if someone could recommend a better approach please share.)
• Added unittests for connect_to_file/pause(simulating the mechanism) / disconnect (simulating the mechanism) / no unittest for TCP connection seemed it would take some time for me I created a ticket to track this https://swift-nav.atlassian.net/browse/CPP-111

Frontend

• Connect button is now checkable, if you are connected and uncheck it will kill the connection to allow for a new one.
• Pause button will pause the current running connection, unchecking will resume (does not process messages during this pause)
• Bottom Nav Bar has a dropdown for TCP/Serial/File. Serial is not implemented yet and all the fields are placeholders for what will be there. TCP and (absolute) Filepaths do work. For quickly connecting to the "test" piksi if the tcp Host/Port fields are blank you can just click connect and it will still connect (until we deem this unnecessary).
• Added a Constants.qml file which we can reference for nested constants, still haven't quite worked out how to pass it down to subfolders/tabs as it is intended to be a single object.

Still need to include delays for files, serial connections, and the refresh rate toggle but I figured itd be better to get this in first.

[notoriaga]

Unless there is some use case for swapping different sender types at runtime I think just making the struct generic is better -

pub struct SolutionTab<S: MessageSender> {
    pub client_sender: S,
    ...
}

I think this might solve the 'static issue as well

[john-michaelburke]

Done. Worked beautifully!!

[notoriaga]

if you have Debug and Clone be supertraits of MessageSender like

trait MessageSender: Debug + Clone {
  ...
}

you can avoid this impl and the + Clone (in one of the tab constructors). Assuming it makes sense to require the sender to be both of those, which seems reasonable

[john-michaelburke]

Done.

[silverjam]

Is this a busy loop?

[john-michaelburke]

Yes it was. I added a 100 ms sleep.