Merge prefix/suffix strings into single strings.

Using guidance from Styling internationalized text in Android, it would be better to combine strings such as "watering_next_prefix" and "watering_next_suffix" to a single "watering_next" plural string.

For example:

<plurals name="watering_needs_prefix">
    <item quantity="one"><b>Watering needs:</b> <i>every day</i></item>
    <item quantity="other"><b>Watering needs:</b> <i>every %d days</i></item>
</plurals>

It would certainly also be fine to use the guidance under "Complex text styling with Annotation", but that's more of a stretch goal. :)