Update docs for 0.16.0 changes

[jennifer-shehane]

• Remove commands Cypress.Cookies.get(), Cypress.Cookies.set(), Cypress.Cookies.remove().
• Add new pages for commands: cy.getCookie(), cy.clearCookie(), cy.setCookie().
• Update cy.getCookies() and cy.clearCookies() commands with new returns.
• Fix wording of cookies before from "remove" to "clear".
• Fix wording of cypress clearing cookies to consistently state we clear cookies "before" each test.
• Update install & running Cypress to new Browser extension workflow.
• Write doc about Cypress & the Browser (how we manage sessions, the use of our extension, etc).

[cypress]

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Test summary

30 • 0 • 0 • 0

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Run details

Project	cypress-documentation
Status	Passed
Commit	1350f78
Started	Aug 6, 2019 5:50 AM
Ended	Aug 6, 2019 5:51 AM
Duration	01:19 💡
OS	Linux Debian - 9.9
Browser	Electron 61

View run in Cypress Dashboard ➡️

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