dev: added pre-commit hooks for code style consistency

See #325

.pre-commit-config.yaml

@@ -0,0 +1,23 @@
+repos:
+-   repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v2.4.0
+    hooks:
+    -   id: trailing-whitespace
+    -   id: end-of-file-fixer
+    -   id: check-yaml
+    -   id: check-added-large-files
+-   repo: https://github.com/pre-commit/mirrors-eslint
+    rev: v7.1.0
+    hooks:
+    -   id: eslint
+        files: client/js/
+        args: ['--fix']
+-   repo: https://gitlab.com/pycqa/flake8
+    rev: '3.8.2'
+    hooks:
+    -   id: flake8
+        files: server/szurubooru/
+        additional_dependencies:
+          -   flake8-print
+        args: ['--config=server/setup.cfg']
+exclude: LICENSE.md