close idaholab#116

This PR adds a new system associated with the syntax block `[SpatioTemporalPaths]`. Multiple SpatioTemporalPath-derived objects
can be added under that syntax block. I have implemented 3 objects so far:

- `PiecewiseLinearSpatioTemporalPath`: This one accepts input file vectors `t`, `x`, `y`, `z` and constructs a spatio-temporal path object.
- `CSVPiecewiseLinearSpatioTemporalPath`: This one is similar to the previous one but instead reads from a csv file.
- `FunctionSpatioTemporalPath`: This one accepts moose functions for `x`, `y` and `z`.

Once a `SpatioTemporalPath` object is constructed, other `MooseObject`s can retrieve path given its name from the warehouse, through the
`SpatioTemporalPathInterface` interface. See e.g. `ADMovingHeatSource` for how that coupling works.

Each spatio-temporal path objects recomputes several path-related information at every time step:

- `SpatioTemporalPath::position()` returns the current path front.
- `SpatioTemporalPath::velocity()` returns the current path moving velocity.
- `SpatioTemporalPath::direction()` returns the current path direction.

Variants of the above methods exist which accepts a time and computes the corresponding path information at the specified time.

By default the path-related information is recomputed at every time step, i.e. the path information is "live".
The users have control over how often the path-related information is updated by the parameter `update_interval`.
There are also methods that retrieve the path-related information from the previous update:

- `SpatioTemporalPath::previousPosition()`
- `SpatioTemporalPath::previousVelocity()`
- `SpatioTemporalPath::previousDirection()`

An object deriving from `SpatioTemporalPath` only need to override one single method `Point position(Real t) const`. Default implementations
are provided for `RealVectorValue velocity(Real t)` and `RealVectorValue direction(Real t)` which use finite-differencing to compute the derivatives.
The developer can optionally override these methods to provide more efficient/accurate implementations.

Utility methods are provided to compute the tangential and normal components of the distance between a given point and the path's current position.

- `SpatioTemporalPath::tangentialDistance(const Point & p)`
- `SpatioTemporalPath::normalDistance(const Point & p)`

Similarly, variants of the above methods exist which additionally accepts a specified time.

Spatio-temporal paths are useful in many scenarios. I have added two concrete examples for demonstration purposes:

- `ADMovingHeatSource` and `ADMovingEllipsoidalHeatSource`
- `SpatioTemporalPathElementSubdomainModifier`

Their names are self-explanatory. Note that `ADMovingEllipsoidalHeatSource` makes use of the tangential and normal distance to effectively "rotate" the ellipsoidal heat source.