Reimplement dialogs as Electron modal windows

[strogonoff]

Dialogs based on Blueprint 3 look okay, but a native dialog window would be much more preferable.

Challenges:

• Modal windows are regular Electron windows
• We’d need to use inter-window communication facilities provided by Electron
• This means passing data to the dialog window via query string somehow, or via ipcRenderer.send(), either directly to dialog window or through main
• After dialog is closed with changes, those changes would have to be again communicated from the dialog window to the main window
• In any case, the data communicated must be a string, or nicely serializable—class instances etc. will not be preserved

[strogonoff]

Side note: we can get rid of dialogs altogether in some data entry cases, by investing some effort into inline input prompts.