Heat generation from frictional energy dissipation

This MR aims to introduce the following features:

1. Consideration of heat generation by frictional energy dissipation between particles.
2. Solve the thermal problem in a given frequency of steps.

The main code modifications are:

• New attribute heatGenerationRatio for the ThermalEngine: When greater than zero, this input parameter is used to calculate heat generation as a given fraction of the energy dissipated by friction.

• New attribute frictDissip for the contact physics: This is used to store the energy dissipation by friction (aka plastic slip work) of individual contacts, which is calculated for each interaction by the Contact Law. This value is later needed by the ThermalEngine to calculate the heat generated in each interaction. P.S.: I created this attribute for physics FricPhys and it is being used only by Law2_ScGeom_FrictPhys_CundallStrack, as this is the law I am currently employing, but I am not sure this is the most appropriate approach.

• New attribute thermalFreq for the ThermalEngine: Similar to thermal.tsSafetyFactor, but used to set the exact number of time steps to solve the thermal problem, i.e., it sets the precise frequency of thermal solution. This feature is activated only when tsSafetyFactor is not used (i.e., tsSafetyFactor<=0).

• Updated check test checkPeriodicThermalConduction to include heat generation.