(core) Add rules to eslint to better match our coding conventions.

Summary:
We used tslint earlier, and on switching to eslint, some rules were not
transfered. This moves more rules over, for consistent conventions or helpful
warnings.

- Name private members with a leading underscore.
- Prefer interface over a type alias.
- Use consistent spacing around ':' in type annotations.
- Use consistent spacing around braces of code blocks.
- Use semicolons consistently at the ends of statements.
- Use braces around even one-liner blocks, like conditionals and loops.
- Warn about shadowed variables.

Test Plan: Fixed all new warnings. Should be no behavior changes in code.

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D2831

app/server/lib/serverUtils.ts

@@ -49,7 +49,7 @@ export function getAvailablePort(firstPort: number = 8000, optCount: number = 20
 export function connect(options: { port: number, host?: string, localAddress?: string, localPort?: string,
                                    family?: number, allowHalfOpen?: boolean; }): Promise<net.Socket>;
 export function connect(port: number, host?: string): Promise<net.Socket>;
-export function connect(path: string): Promise<net.Socket>;   // tslint:disable-line:unified-signatures
+export function connect(sockPath: string): Promise<net.Socket>;
 export function connect(arg: any, ...moreArgs: any[]): Promise<net.Socket> {
   return new Promise((resolve, reject) => {
     const s = net.connect(arg, ...moreArgs, () => resolve(s));