Upgrade build process from gulp to webpack

[ryanio]

Description

This PR upgrades the build process from gulp/browserify to webpack.

This PR also:

• Removes npm run build-all for creating sub-package browser builds.
  • These builds weren't being published, and we aren't aware of many people using them.
  • They didn't have proper test coverage to ensure integrity of the builds (web3.min.js is tested in both chrome and firefox with karma)
  • It is now easy for anyone to create a browser build of a sub-package with this PR. Just modify the root webpack.config.js and update the entry and library to point to the sub-package you would like to build, then run npm run build.
• Updates some root deps and removes old/unneeded ones
• Updates readmes var => const/let

Type of change

• build process enhancements (non-breaking change)

Checklist:

• I have selected the correct base branch.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• Any dependent changes have been merged and published in downstream modules.
• I ran npm run dtslint with success and extended the tests and types if necessary.
• I ran npm run test:unit with success.
• I ran npm run test:cov and my test cases cover all the lines and branches of the added code.
• I ran npm run build and tested the resulting files from dist folder in a browser.
• I have updated the CHANGELOG.md file in the root folder.
• I have tested my code on the live network.
• I have checked the Deploy Preview and it looks correct.

[coveralls]

Coverage remained the same at 90.166% when pulling a049118 on upgrade-to-webpack into 1404086 on 1.x.

[cgewecke]

Looks good! Great improvement 🥇

Wrt dist/web3.min.js...do we usually merge changes to that on release?

[ryanio]

@cgewecke thanks! hm yes that makes sense to me, so i can remove it from this PR. edit: done