samples: Use API 23 by default, except for N-specific samples.

Since N is still in DP4, but we're building docs from nyc-dev now,
adjust build so that most samples are built using flags for API 23.
N-specific samples have overrides added in template-params.xml.

Also adjusted build tools version to 23.0.3. (I thought I'd done this
earlier.)

Change-Id: I567e5c443cdb107ef4465aaded7481998943b000
1 file changed