Distinguish between the first and innermost axis.

The fix for #1056 caused a regression where grid lines were drawn for
the innermost axes on both sides instead of just the first axis.
Fixed by properly distinguishing the first axis in each direction from
the innermost one on each side.  Fixes #1075.
Don't add padding when there's no last tick.

Flot 0.8 added logic to account for the size of axis tick labels and add
padding around the edges of the plot, to prevent long labels from
sticking out.  But it padded both sides equally, which is incorrect if
the right/top side has no last axis label.

Fixed by allocating padding per-side, and checking whether the last
label would be shown before padding the top or right.  Fixes #1048.
Default lineHeight based on the font size.

Flot 0.8.0 used the default font size, typically derived from the
placeholder, as the basis for the default lineHeight.  This produced
incorrect results when a font.size was provided explicitly, and it
differed from the placeholder’s CSS size.

Fixed by waiting to default lineHeight until the actual font size has
been resolved.  Fixes #1131.
Merge pull request #1198 from dnschnur/axis-grid-fix

Distinguish between the first and innermost axis.
Merge pull request #1199 from dnschnur/line-height-default-fix

Default lineHeight based on the font size.
Merge pull request #1200 from dnschnur/xaxis-plot-size-fix

Don't add padding when there's no last tick.