(core) Speed up and upgrade build.

Summary:
- Upgrades to build-related packages:
  - Upgrade typescript, related libraries and typings.
  - Upgrade webpack, eslint; add tsc-watch, node-dev, eslint_d.

- Build organization changes:
  - Build webpack from original typescript, transpiling only; with errors still
    reported by a background tsc watching process.

- Typescript-related changes:
  - Reduce imports of AWS dependencies (very noticeable speedup)
  - Avoid auto-loading global @types
  - Client code is now built with isolatedModules flag (for safe transpilation)
  - Use allowJs to avoid copying JS files manually.

- Linting changes
  - Enhance Arcanist ESLintLinter to run before/after commands, and set up to use eslint_d
  - Update eslint config, and include .eslintignore to avoid linting generated files.
  - Include a bunch of eslint-prompted and eslint-generated fixes
  - Add no-unused-expression rule to eslint, and fix a few warnings about it

- Other items:
  - Refactor cssInput to avoid circular dependency
  - Remove a bit of unused code, libraries, dependencies

Test Plan: No behavior changes, all existing tests pass. There are 30 tests fewer reported because `test_gpath.py` was removed (it's been unused for years)

Reviewers: paulfitz

Reviewed By: paulfitz

Subscribers: paulfitz

Differential Revision: https://phab.getgrist.com/D3498

app/client/ui2018/modals.ts

@@ -1,6 +1,6 @@
 import {FocusLayer} from 'app/client/lib/FocusLayer';
 import {reportError} from 'app/client/models/errors';
-import {cssInput} from 'app/client/ui/MakeCopyMenu';
+import {cssInput} from 'app/client/ui/cssInput';
 import {prepareForTransition, TransitionWatcher} from 'app/client/ui/transitions';
 import {bigBasicButton, bigPrimaryButton, cssButton} from 'app/client/ui2018/buttons';
 import {colors, mediaSmall, testId, vars} from 'app/client/ui2018/cssVars';