Implement heat transfer

[acodcha]

Implement heat transfer quantities:

• PhQ::HeatTransfer (units of energy)
• PhQ::SpecificHeatTransfer (units of energy)
• PhQ::MolarHeatTransfer (units of energy)
• PhQ::HeatTransferRate (units of power)
• PhQ::SpecificHeatTransferRate (units of power)
• PhQ::MolarHeatTransferRate (units of power)

Requires #193