Support closing add source view with dedicated cancel button

[crystoneme]

when I open the software, but without load any models, I can't find anywhere to exit.
Until I forced to kill it in the system setting.

[alexrozanski]

Hey @crystoneme - yeah this isn't ideal - the window is presented as a standard macOS sheet which can only be dismissed with the Esc key. Let me look into improving this though, I could add a dedicated close button perhaps.

[alexrozanski]

@crystoneme this is fixed in 8f203df, will release this soon!

[alexrozanski]

Fixed in v1.2.0