fix confirm prompt when invalid locale used with number selection

[johnataylor]

Fixes #648

Description

Confirm prompt had exception when invalid locale used with number selection.

(I'm also aligning the implementation slightly with the c# - calling the variable culture.)

Note the defaults tables should be merged - however they are public - they shouldn't be public. We can treat this as a separate issue.

[coveralls]

Pull Request Test Coverage Report for Build 2205

• 11 of 11 (100.0%) changed or added relevant lines in 1 file are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.07%) to 82.087%

---

Files with Coverage Reduction	New Missed Lines	%
libraries/botframework-config/src/botConfigurationBase.ts	2	85.59%

Totals
Change from base Build 2201:	-0.07%
Covered Lines:	2630
Relevant Lines:	3085

---

💛 - Coveralls

[stevengum]

Some minor linting, and question about the deteremineCulture() method.