Code nav: do not tokenize code views on Bitbucket

Created by: chrismwendt

Motivation: some code hosts have already tokenized the code view (e.g. Bitbucket). The tokenization currently prevents text selection from working on Bitbucket https://github.com/sourcegraph/sourcegraph/issues/4051

Implementation: this adds a boolean codeViewsRequireTokenization to the CodeHost interface, and passes it to codeintellify.

Depends on https://github.com/sourcegraph/codeintellify/pull/115

Test plan:

• Run Bitbucket locally
• Open a file
• Make sure text selections work

Fixes https://github.com/sourcegraph/sourcegraph/issues/4051

Slack conversation https://sourcegraph.slack.com/archives/CHXHX7XAS/p1559599129008000