add geo alignment support for the TRD system

Add geometry alignment support for the TRD detectors in view of analyzing the mCBM 2022 data. A list of other minor changes are included in this MR, too small to make the subject of individual requests like:

• documentation change (observed by Eloin)
• Adding user function to the Trd cluster
• Adding time offset for TRD2D hit definition

The code should work with a new macro for defining misalignments
"macro/beamtime/mcbm2022/create_alignment_2022_05_23_nickel.C" which should be finalized by @d.ramirez

The MR should be also interesting for @apuntke and @p.kaehler

core/data/trd/CbmTrdCluster.cxx

@@ -128,6 +128,25 @@ int32_t CbmTrdCluster::IsChannelInRange(int32_t ch) const
   return 0;
 }
 
+//____________________________________________________________________
+uint16_t CbmTrdCluster::GetSize() const
+{
+  uint16_t size(0);
+  if (HasFaspDigis()) {
+    size = GetNCols() << 1;
+    if (HasOpenStart()) size--;
+    if (HasOpenStop()) size--;
+    if (size <= 0) {
+      LOG(warn) << GetName() << "::GetSize: Fasp cluster meta-info corrupt.";
+      std::cout << ToString();
+      return 0;
+    }
+  }
+  else
+    size = GetNCols();
+  return size;
+}
+
 //____________________________________________________________________
 bool CbmTrdCluster::Merge(CbmTrdCluster* second, bool typ)
 {