Add tools attributes to set extreme values for NumberPicker

tools:minValue and tools:maxValue can now be used to specify
the min and max values of a NumberPicker in the layout editor.

Bug: http://b.android.com/205084
Change-Id: I10037726346c82ca3cf84d255727b84a12ac0349
(cherry picked from commit 3c2b1c65c907fa4f2cae102507688fd0bffd1b24)