[DONE] A11y for caption_maker (#982)

* * Change TRANSCRIPTION_STT_SENTENCE_MAX_LENGTH default value to 2s
* Now caption-maker textareas are limited to 40 chars max per row, with max chars at 80
* When editing a caption/subtitle, the player auto-seek at related time
* add missing aria-hidden + aria-label on some button-icons
* Uniformize caption/subtitle naming
* Reorder CSS for code styling

* Add .po lang files

* Add missing JsDocs on caption_maker.js
+ Add .eslintrc.js to lint JS errors/warnings

* Add client Validation to caption maker for better ergonomy

* last minor corrections

* Add a minor code comment + rename some vars.

.eslintrc.js

@@ -0,0 +1,41 @@
+module.exports = {
+  "env": {
+    "browser": true,
+    "commonjs": true,
+    "es2021": true,
+    "node": true
+  },
+  "extends": "eslint:recommended",
+  "parserOptions": {
+    "ecmaVersion": "latest",
+    "sourceType": "script"
+  },
+  "rules": {
+    "indent": [
+      "error",
+      2,
+      {"SwitchCase": 1}
+    ],
+    "linebreak-style": [
+      "error",
+      "unix"
+    ],
+    "semi": [
+      "error",
+      "always",
+    ],
+    /*"camelcase": ["warn", {"ignoreGlobals": true}],*/
+    /* First capital letter is reserved for "new" Objects. */
+    "new-cap": ["warn", { "capIsNew": true }]
+  },
+  /* functions and Objects that will not trigger a "not defined" error. */
+  "globals": {
+    "Cookies": "readonly",
+    "gettext": "readonly",
+    "interpolate": "readonly",
+    "bootstrap": "readonly",
+    "videojs": "readonly",
+    "send_form_data": "writable",
+    "showalert": "writable",
+  }
+};