Add KernelConcept to document and check kernel requirements

Following some brief discussion in #347, `kernel_2d` and `kernel_2d_fixed` defined in Numeric may not be as well documented as users may expect. For example,

- Are the kernel types singular or dual mode: 1D and/or 2D
- Since they are used in both, 1D and 2D convolution operations, are there any particular requirements and restrictions for each of use cases?

Ideally, if there are `KernelConcept`-s that capture all the details.