Let a planar quadrangle $ABCD$ satisfy $AB = BC$ and $CD = DA$. Compute a point $P$ such that $PA+PB+PC+PD$ is minimum, for each of following two cases.
- The inner angle of $B$ is greater than $\pi$ but less than $2\pi$.
- All the inner angles of $A$, $B$, $C$ and $D$ are less than $\pi$ but greater than $0$.