Fix all strict errors in /client (#1489)

## Description:

Second PR to fix issues in order to enable strict mode.

## Specifics

1. Most important change: Turned off errors for Class variables not
initialized in constructor. I've noticed that pretty much all Classes in
the project have at least one occurence of that issue. And fixing it
properly would require a large refactor across the whole project. So
disabling the rule seems like a good solution in this case.

#1075 

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I have read and accepted the CLA aggreement (only required once).

## Please put your Discord username so you can be contacted if a bug or
regression is found:

azlod

tsconfig.json

@@ -20,7 +20,8 @@
     "experimentalDecorators": true,
     "resolveJsonModule": true,
     "strictNullChecks": true,
-    "useDefineForClassFields": false
+    "useDefineForClassFields": false,
+    "strictPropertyInitialization": false
   },
   "include": [
     "src/**/*",