Add config file for LGTM (#681)

Disable false positives that cannot be fixed by LGTM, because their
heuristic detects strings such "id" that are actually very common in
DICOM, for example in "UID".

lgtm.yml

@@ -0,0 +1,4 @@
+---
+queries:
+  # https://lgtm.com/rules/1510014536001/
+  - exclude: py/clear-text-logging-sensitive-data