[Feature requests] OAK Device Manager

[Erol444]

A few feature/bug fix requests for the OAK device_manager.py (docs here):

• Currently the app stores reference to DeviceInfo after selecting the device, instead of storing the actual Device reference. This means that for each command, app has to "re-connect" to the OAK device.
• Sometimes when pressing Flash configuration it will throw error in terminal due to XLINK_CLOSE_STREAM_RESP (might be releated to issue above)
• Expose to GUI the following functions added to the DeviceBootloader: flashCustom, readCustom, flashGpioModeBootHeader, flashUsbRecoveryBootHeader, getMemoryInfo - likely in a new tab
• Expose to GUI the following functionalities from the DeviceBase: getCameraSensorNames (nice to have), read facotry/calibration either as .bin or .json - likely in a new tab
• Add testing for POE speed. Code here.
• Fix: when device is not found, it still tries to query it's type/version/etc., so it throws 3 error popups in a row: X_LINK_DEVICE_NOT_FOUND , NONE TYPE object has no attribute 'GET TYPE', NONE TYPE object has no attribute 'isEmbeeded Version'

[Erol444]

#662 PR addresses 2/3 of these issues (bugfixes)

[Erol444]

OAK Device Manager will be moved into depthai-viewer (https://github.com/luxonis/depthai-viewer)

[themarpe]

CC: @zrezke