Dev additions

[mattkrau]

As talked about in the weekly meeting, rebased to master:

Adds following functionalities:

• Scans for Subresource Integrity Check
• Additional scans for serverleaks
• Reading of GeneratorTags

[hprid]

Thank you for your pull request. We discussed most of it already in person, but for the record here are the most important points:

• Keep your code PEP8 compliant (with an exception of line length, which can be about 90).
• Use different branches for different features and provide several pull requests. This helps to review individual changes and makes discussions easier, since every discussion belongs to one topic.
• Resolve all conflicts and rebase your branch to the current master.

Regarding SRI

• Do not add pseudo headers to the security headers. Instead, provide these information in the dictionary that is already returned for the CSP header.
• Search for script/style tags and their integrity attribute and provide a list of resources that include and/or miss SRI. Include whether SRI failed (you can consider the block reason of a failed request, see Page.failed_request_log).
• When searching for nodes, use the scripts_disabled context manager to avoid changes to the DOM while searching.

Regarding the generator tag

• Remove code that is not used and rename variables that were copied from other codes and give them names matching the context.
• You do not need to use the search function to search the page for "Generator". Instead, you can use a more specific selector, e.g., meta[name="generator" i]. This will return all nodes you are interested in
• When search for nodes, use the scripts_disabled context manager to avoid changes to the DOM while searching.

Regarding additional serverleaks

• _match_package_file uses "binary or" in the loop instead of "logical or". You could replace this loop with the any function together with an generator expression, i.e., return any(target in content for target in targets). Use the beauty of Python :-)