Fix pin assignments

[mdbartos]

Some of the pin assignments have gotten disorganized or lost through the firmware iterations:

• optical_rain_pwr lost its pin assignment
• optical_rain_rx lost its pin assignment
• Pin_Sampler_Sampler_Count lost its pin assignment

Moreover, @ndajeng suggests switching the pin assignment for the autosampler:

• Pin_Sampler_Power on P3[3] (VDD)
• Pin_Sampler_Trigger on P3[2]

[mdbartos]

optical_rain_pwr temporarily moved to P3[5]
optical_rain_rx temporarily moved to P0[5]

[mdbartos]

Note that the bottle count currently cannot be obtained because Pin_Sampler_Sampler_Count lost its assignment.