* Replace `ormconfig.js` with a newer mechanism of configuring
TypeORM that can be included in the source code properly.
The path to `ormconfig.js` has always been awkward to handle,
and eliminating the file makes building different Grist setups
a bit simpler.
* Remove `electron` package. It is barely used, just for some old
remnants of an older attempt at electron packaging. It was used
for two types, which I left at `any` for now. More code pruning is
no doubt possible here, but I'd rather do it when Electron packaging
has solidified.
* Add a hook for replacing the login system, and for adding some
extra middleware the login system may need.
* Add support for some more possible locations of Python, which
arise when a standalone version of it is included in the Electron
package. This isn't very general purpose, just configurations
that I found useful.
* Support using grist-core within a yarn workspace - the only tweak
needed was webpack related.
* Allow an external ID to be optionally associated with documents.
