Adding logicalKeyboardKeyTriggers and showDatePickerOnFocus

[Honeyman-Applications]

Adding logicalKeyboardKeyTriggers, and showDatePickerOnFocus

• This allows any keys on a physical keyboard to open the date picker
• when showDatePickerOnFocus is true the date picker opens automatically (usually after tab, or next)
• showDatePickerOnFocus is defaulted to false for backwards compatibility
• The default spacebar to open date picker is left in place for backwards compatibility
• I also deleted the platform specific code in the example, because the content in there was causing compiling errors.
• The platform specific code can be generated using flutter create . when run from the example directory
• added documentation in the README, and CHANGLOG, and ran the auto formatter
• added SingleChildScrollView in example to avoid overflow
• added example of the new features