update analysis.bat.BAT to use .results

[orbeckst]

Follow the new AnalysisBase API and store results in analysis.bat.BAT in .results instead of class attributes.

See omnibus issue #3261 for background and details. See PR #3263 as an example (DensityAnalysis) but note that no deprecations are needed (new in 2.0.0)

• put all generated data into self.results instead of self
• keep managed attributes in place with deprecation message
• add an entry in CHANGELOG under Changes (for completeness)