Implement context isolation in electron

[grctest]

Is your feature request related to a problem? Please describe.

We're not yet following Electron best practices fully. https://www.electronjs.org/docs/latest/tutorial/context-isolation

Describe the solution you'd like

https://github.com/beetapp/beeteos/blob/master/src/background.js#L170
https://github.com/beetapp/beeteos/blob/master/src/background.js#L251

Set nodeIntegration and enableRemoteModule to false, and contextIsolation to true.

Adapt renderer to request node/module functions/data through the ipcmain/ipcrenderer pipeline.

Describe alternatives you've considered

Exhaustively prevent XSS in the renderer.

Additional context

Latest BTS NFT Viewer has made these changes: https://github.com/BTS-CM/NFT_Viewer

So has the airdrop tool: https://github.com/BTS-CM/airdrop_tool

The background.js file is likely to significantly bloat due to inheriting code from the renderer.

This is likely a multi-thousand LOC feature request, however it's worthwhile to make the wallet follow best practices.

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This is an issue inherited from the Beet repo: bitshares#261

By addressing this exclusively for EOS we will not only improve security best practices, but we will also demonstrate the proof of concept for the main Beet wallet to follow suit.

[grctest]

Context isolation has been fully implemented now: https://github.com/beetapp/beeteos/releases/tag/v1.1.0