SF Features#114: Increase the time limit for the Tile Age and use days in the GUI.

The limit is now increased to 1 year.
Units are the more human friendly scale of days, rather than trying to deal in hundreds of thousands of seconds.
Values are still held in seconds in the preferences.
[QA] Fix issue spotted with cppcheck 1.59
SF Bugs#99: Increase limit for Map IDs

Change from a guint8 to a guint16 to enable larger map id range.
Thus prevents silently auto wrapping numbers around which may then overwrite a different map cache.
SF Bugs#97: Fix missing redownload settings of some maps in the example config

Some extra properties of the maps should be defined to enable redownload behaviour.
[i.e. match the built in settings in osm.c]
Add ability to use a conversion function between the displayed widget contents and the value stored internally.
SF Bugs#100: Fix Crash on viewing Track Properties with extreme gradients.

Even though the code checked for end of the array, it did not set the index value correctly.
Thus it could access memory outside of the array, which could be zero and lead to divide by zero errors.

Refactor the code to use the common chunk index function.
Refactor Track property grid drawing into a common function.

Change the y-axis text to be slightly smaller to accommodate displaying larger values.
Otherwise distance labels over '100 miles' may be seen fully.
SF Bugs#101: Fix Acquire from Google Directions.

Allow for some download redirects by default. Otherwise may get HTTP 302 errors.