Rework txsgui

This MR builds on !15 (closed) and proposes a major rework of the txs GUI.

As it is now, it is available as the txs2 command so that previous and current GUI can be launched. Most of the widgets and direct signal/slot are handled in the .ui file. When needed (e.g., for the plots), widgets are "promoted" to the relevant widgets in txs.app. The analysis is run in a separate process, this allows to stop the processing with Ctrl-C.

Here is a screenshot:

I had to make this patch to make it work locally:

--- a/txs/datasets.py
+++ b/txs/datasets.py
@@ -547,7 +547,7 @@ class BlissDataset:
                     if self.detector in data[f"{scan}/measurement"].keys():
                         scan_number = int(scan.split('.')[0])
                         scan_folder = glob(
-                            f"{exp_root}/RAW_DATA/{sample_id}/{dset_id}/"
+                            f"{exp_root}/*/{sample_id}/{dset_id}/"
                             f"scan{scan_number:04}"
                         )