[Roadster] basic POI spec

[Ian McIntosh]

Here's a basic spec.  Now's the time to speak up if you have any other
ideas!

-Ian

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POI (point of interest) and POI Sets:

- Each POI belongs to exactly one POI Set.

- Each POI set will have an icon associated with it.  XXX: Can
individual POI have a custom icon?

- All POI Sets are listed in the "POI" tab of the sidebar, each with a
checkbox.

- XXX: Can POI Sets be children of other POI sets?  Or is each POI Set
in a category?

- A POI Set is made a Visible POI Set by clicking the checkbox next to
the set on the "POI" tab of the sidebar.

- The mouse cursor will change to the standard "hovering over link"
cursor (from web browsers) when over a POI icon.

- A POI is made a Highlighted POI by double-clicking on it in the result
list OR by single-clicking(?) its icon on the map.

- A Highlighted POI can be turned back into a non-highlighted POI by
doing either of the above actions again, or by clicking an X in the Info
Balloon.

==========
Rules for drawing:

- When zoomed in "enough", we draw icons for all POI from Visible POI
Sets.

- When not zoomed in "enough", only icons for (A) the one POI that is
currently selected in the search results list and (B) any Highlighted
POI, are shown.

- All Highlighted POI will have a big Info Balloon.  If a POI is not
Highlighted but is the currently selected result in the search results
list, a Mini-Label is used to mark the location.  At no time will both
be shown.

- A Mini-Label cannot be closed (except by hacks: de-selecting the
search result with ctrl-click or clearing the search results by
searching for a blank string: "").  But of course, if the user selects a
different search result, the new result will be marked with the
Mini-Label instead.

- If the current search result is an address, the spot is always marked
with a Mini-Label (no Info Balloons for addresses).

- The Info Balloon contains the following POI data: Name, Address,
Phone, and clickable links for [web] (if a value for "web-url" is
present) and [edit], which will bring up the POI editor.  When routing
is implemented, it will have "Directions: [To here] - [From here]"
links.

- More than one POI can be a Highlighted POI and thus multiple Info
Balloons can be visible at once.  They will do their best to not overlap
each other.

- The Mini-Label shows just the POI's Name (in the case of a road
result, a basic dot icon is used and the "name" is the full address, eg.
"441 Stuart St., Boston, MA, 02116").