UI: Remove m_pTraceWriter since it was not being used and was causing an unnecessary file to be created on disk

(cherry picked from commit 50056dbe31ee4c78aac1c073526495166a1d55bd)
UI: Fix support for taking snapshots after an edited & outdated snapshot.
* Also fix algorithm that finds the previous snapshot for diff'ing purposes so that it only returns valid snapshots.

(cherry picked from commit 9734f7d774470c4efe2cc0b9858d873fcc55850d)
UI: Fix unnecessary memory overhead when loading traces.
* A vogl_trace_packet can have lots of memory associated with it, so they should not be copied or assigned if it can be avoided. In this case, the loading was using a single trace packet instance to load the data from disk, then the packet was being copied into its associated node in the API call tree. This assignment / copy was temporarily (and unnecessarily) doubling the size of the packet, requiring extra memory allocations, and generally just causing excessive overhead. Instead, allocate a separate vogl_trace_packet for each packet that needs to be loaded from disk, and pass that memory off the apiCallItem for management. This greatly improves load times and allows us to load traces that would previously fail due to memory limitations.
* Also move a few allocations over to using vogl_new and vogl_delete so that vogl can track the memory usage.

(cherry picked from commit 1bcaf8bd911c1b1604e59898c752506be1394c38)
UI: separate capturing of vogl_gl_state_snapshot from allocation of the vogleditor_gl_state_snapshot for better error reporting and memory management

(cherry picked from commit 12ec6a58517055d2e460bfc0d06d1847931bf7d0)