Epan+Qt: Invalidate cached column strings.

Epan+Qt: Invalidate cached column strings.

Add col_data_changed, which checks to see if we have updated column
info. Add col_append_frame_number, which adds a frame number and sets
col_data_changed. Call col_append_frame_number instead of
col_append_fstr from some dissectors.

Add PacketListRecord::invalidateAllRecords, which invalidates any cached
record data. Add PacketListModel::invalidateAllColumnStrings which calls
invalidateAllRecords and signals that our data has changed. Call
invalidateAllColumnStrings when we have new name resolution or column
information.

Bug: 11414
Bug: 11468
Change-Id: I2671594a722f4f9436fe1df84d43489a148e0cee
Reviewed-on: https://code.wireshark.org/review/26373
Reviewed-by: Gerald Combs <gerald@wireshark.org>
Petri-Dish: Gerald Combs <gerald@wireshark.org>
Tested-by: Petri Dish Buildbot
Reviewed-by: Roland Knall <rknall@gmail.com>