[TRANSFORM] Generalize from past scalar to past any linear op (this was supported, but restricted). Fix node sorting problem, by iterating over a copy list of the node instead of iteration over graph.node. Fix corner case when both branches are empty and come from the same node

LabelSelect is currently broken for signed inputs
will open issue separately

[Transformation] Add warning if chosen clock period could lead to failure due to clock divider constraints

[Transformation and Test] Add option to adjust clock frequency in ipstitch and when making the pynq project get fclk from the metadata properties. Change tfc w1a1 test to test new feature

use None in util fxn to indicate no file output

[HLSCustomOp] Refactoring fpgadataflow custom ops by adding comments and adding two functions to base class