Fix two typos in the description of FlaskGroup.
Remove two redundant empty lines.

PEP8 suggests to use two empty lines to separate functions, not three.
Change `== None` to `is None`.

PEP8 (E711) suggests that comparison to None should be `cond is None`.
Put two spaces before inline comments when there is only one space.

PEP8 (E261) suggests to use at least two spaces before inline comments.
Unify the uses of "testsuite" vs "test suite".

Use "test suite", which is more prevailing in the source code.
Unify the uses of "file system" vs "fileystem".

Use "filesystem", which is more prevailing in the source code.
Unify the uses of "urls" vs "URLs".

Use "URLs", which is more prevailing in the source code.
Fix a typo in the description of SecureCookieSession.

The term "base class" (with a space) is used in another file, so use it here as well to make the wording consistent across the whole project.
Add a missing period in the description of the signals module.
Unify the uses of "sourcecode" vs "source code".

Use "source code", which is more grammatically correct.
Fix a typo in a comment in MethodViewType.__new__.
Remove a redundant "the" in a comment.
Merge pull request #1225 from s3rvac/typo-and-cosmetic-fixes

Typo and cosmetic fixes