Two Manganese(II)-Based Hybrid Multifunctional Phase Transition Materials with Strong Photoluminescence, High Quantum Yield, and Switchable Dielectric Properties: (C<sub>6</sub>NH<sub>16</sub>)<sub>2</sub>MnBr<sub>4</sub> and (C<sub>7</sub>NH<sub>18</sub>)<sub>2</sub>MnBr<sub>4</sub>