Limiter for Javascript Output, Tests, Formatting

[phutelmyer]

Describe the change
With no limits set for the string fields (e.g., tokens, strings) in ScanJavascript, events have been observed with well over thousands of objects in their associated fields. While this may be useful for some use cases, by default it may be advisable to not collect so many objects. The following modification were implemented:

• Default limit (50) for amount of strings per field to be collected from ScanJavascript session. Configurable in backend.yml
• Strings are distinct

The following fields are limited:

• tokens
• keywords
• strings
• identifiers
• regular_expressions

Describe testing procedures
Created test: test_scan_javascript_character_limits in test_scan_javascript.py that ensures that the limit functions properly.

Sample output

...
          "tokens":[
                "BlockComment",
                "String",
                "Punctuator",
                "Keyword",
                "Identifier",
                "LineComment",
                "RegularExpression",
            ],
            "keywords":[
               'throw', 
               'return', 
               'else', 
               'var', 
               'new'
            ]
...

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of and tested my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

[ryanohoro]

👍