Replace phantomjs with chromote as headless browser

[siddhesh195]

chromote browser can be used as headless browser for testing instead of phantomjs

Discussion on why chromote is suitable choice of browser: https://github.com/animint/animint2/pull/82

Using chromote cause the following test failures:

(test-renderer3-update-axes.R:46:1) (test-renderer3-update-axes-multiple-ss.R:75:1) (test-renderer3-tooltip-interactivity.R:12:1 (test-renderer3-path-key.R:49:3) (test-renderer2-widerect.R:229:1) (test-renderer2-PredictedPeaks.R:126:1) (test-renderer1-variable-value.R:171:3) (test-renderer1-url-fragment.R:35:1) (test-renderer1-global-variables.R:25:3) (test-renderer1-geom-text-color.R:20:1) (test-renderer1-facet-lines.R:50:1)

Please note that these test cases are failing only for chromote.

The above failures are caused because the following helper functions are not compatible with chromote and need to be changed to work with chromote:

1. clickHTML
2. clickID
3. expect_rotate_anchor