Change the names for feature extraction classes from Snake Case to Pascal Case

[suhaibmujahid]

The following files contained such classes:

• bugbug/bug_features.py
• bugbug/commit_features.py
• bugbug/issue_features.py
• bugbug/test_scheduling_features.py

In the following example, source_code_file_size should be renamed to SourceCodeFileSize:

bugbug/bugbug/commit_features.py

Lines 39 to 46 in 9021149

	class source_code_file_size(object):
	def __call__(self, commit, **kwargs):
	return {
	"Total code files size": commit["total_source_code_file_size"],
	"Average code files size": commit["average_source_code_file_size"],
	"Maximum code files size": commit["maximum_source_code_file_size"],
	"Minimum code files size": commit["minimum_source_code_file_size"],
	}