…` as `PolymerElement` (#367)

* Rename 'polymer.html' to 'polymer-legacy.js'.

* fix the convertedFilePath logic

* Scope 'polymer.html' -> 'polymer-legacy.js' renaming to packages named 'polymer'.

* add rewrite logic for Polymer.Element -> PolymerElement

* wip - stop sharing a top-level includes, run package-relative always

* Fix comment to more clearly indicate that it's pointing out a bug, not intended behavior.

* Clean up name replacements.

* reformat tests

* Explicitly test 'polymer.html' -> 'polymer-legacy.js' renaming both with and without the './' prefix.

* Test that only files named 'polymer.html' at the root of the package are renamed.

* Remove unnecessary quote escapes.

* Add `getScriptConvertedFilePath` to convert `OriginalDocumentUrl`s of files which were already scripts to `ConvertedDocumentFilePath`s.

* fix polymer override check

* whoops, fix the fix for polymer-legacy renaming

* Fix conversion functions in PackageUrlHandler; always scan all dependencies of a package during conversion.

* Fix `PackageUrlHandler`'s `getOriginalPackageNameForUrl` and `packageRelativeConvertedUrlToConvertedDocumentFilePath`.

* Revert removed filtering in package scanner.

* fix the shady-unscoped-style-import-css.html issue

* Entrypoints for packages can be given in `ConversionSettings`; `ProjectScanner` defaults to reading entrypoints from 'bower.json'; update tests with entrypoint mappings.

* Remove unused `analyzer` parameter from `createDefaultConversionSettings`.

* Remove commented code; `x ? x : y` -> `x || y`; update tests. (...)

- Tests: `convert`'s `entrypoints` property in the arguments object now requires
  that the user completely replaces the map, rather than automatically adding a
  "some-package" entry, if one isn't in the given map.

* `PackageScanner#scanDocument`: replace optional `forceJs` parameter with required `scanAs` parameter.

* Set entrypoints for new tests from master.

* Handle cases where 'bower.json' does not exist in a package, causing an error to be thrown.

* Fix `PackageUrlHandler#getPackageDir`.

* Add new `entrypoints` conversion option to tests.

* `entrypoints` -> `packageEntrypoints`

* Add comments at the point the 'polymer.html' -> 'polymer-legacy.html' renaming happens.

* Update fixtures.

* update CHANGELOG.md

* Update example in README.md .

* Claim added TODO.