Move time formatting to BTimeformat.

* Harmonize API for all B*Format to take an output BString by reference
as the first parameter,
* Move the FormatTime methods from BLocale to BTimeFormat
* Adjust all callers for BTimeFormat, BTimeUnitFormat and
BDurationFormat.

Adjust all BDateFormat callers again.

BDateFormat: improve API

* Use a reference rather than a pointer for the output string, removing
the need for NULL checks (which were missing, anyway)
* Adjust callers to that change
* Add new Format variant taking a BDate argument

Move date formatting from BLocale to BDateFormat

* There is a little code duplication. This will be moved to BFormat once
the time and datetime formatting is also moved out of BLocale
* The way to create a BDateFormat from a BLocale is still open for
discussion. I'm undecided between making BDateFormat a member of
BLocale, or adding a BDateFormat(const BLocale&) constructor.
* Adjust all users of the API.

Further simplify the Time tooltips by using SetToolTip.

Don't constantly recreate the tool tip, just update the text.

Fixes #9502, more or less.

Create TimeZoneListView class and move GetToolTipAt into it, fixes #7726

Signed-off-by: Matt Madia <mattmadia@gmail.com>

Move time formatting to BTimeformat.

* Harmonize API for all B*Format to take an output BString by reference
as the first parameter,
* Move the FormatTime methods from BLocale to BTimeFormat
* Adjust all callers for BTimeFormat, BTimeUnitFormat and
BDurationFormat.

Adjust all BDateFormat callers again.

BDateFormat: improve API

* Use a reference rather than a pointer for the output string, removing
the need for NULL checks (which were missing, anyway)
* Adjust callers to that change
* Add new Format variant taking a BDate argument

Move date formatting from BLocale to BDateFormat

* There is a little code duplication. This will be moved to BFormat once
the time and datetime formatting is also moved out of BLocale
* The way to create a BDateFormat from a BLocale is still open for
discussion. I'm undecided between making BDateFormat a member of
BLocale, or adding a BDateFormat(const BLocale&) constructor.
* Adjust all users of the API.

Further simplify the Time tooltips by using SetToolTip.

Don't constantly recreate the tool tip, just update the text.

Fixes #9502, more or less.

Create TimeZoneListView class and move GetToolTipAt into it, fixes #7726

Signed-off-by: Matt Madia <mattmadia@gmail.com>