The icon_image_alt column in both the host and service tables contains
an image alt text. However, because it is defined as a varchar(32), many
alt texts do not fit. The type has been expanded to text, as with most
free text fields.
Closes#752.
When defining a TimePeriod, the maximum length of a range value was
capped at 255 characters. This limitation has now also been removed by
switching to the Text type.
Closes#724.
While re-reading the schema, I stumbled upon some missing
properties_checksum comments that were also added.
