feat: ability to load characters and their skills from ESI (#25)

This can track multiple characters, and tries to make as few as possible
ESI calls.

In the localstorage, we keep track of all the characters and their
refresh-tokens.
Access-tokens and skills are not stored in the localstorage, which means
that every reload, this information is fetched from ESI again.

src/EsiCharacterSelection/EsiCharacterSelection.module.css

@@ -0,0 +1,25 @@
+.character {
+    width: 100%;
+}
+
+.character > select {
+    background-color: #1d1d1d;
+    color: #c5c5c5;
+    height: 24px;
+    width: calc(100% - 20px);
+}
+
+.character > button {
+    background-color: #1d1d1d;
+    color: #c5c5c5;
+    cursor: pointer;
+    height: 24px;
+    text-align: center;
+    width: 20px;
+}
+
+.character > button.noCharacter {
+    text-align: left;
+    padding-left: 5px;
+    width: 100%;
+}