Update Events (#10)

This update restructures the events page code and provides additional functionality.
- Overwrite old entries on re-submission of previously used emails
- Build data and stats caches on launch for use in submission checks and stats regeneration
- Update to form content
- Move stats function to separate utils file

Reviewed-on: ayo/website#10
Co-authored-by: Jimmy Vargo <james@ayo.tokyo>
Co-committed-by: Jimmy Vargo <james@ayo.tokyo>

events/templates/form.html

@@ -57,6 +57,21 @@
 				<input id="other-text" type="text" placeholder="Other その他" />
 			</div>
 
+			<div class="question">
+				<input id="presentation-interest" type="checkbox" />
+				<label for="presentation-interest">I'm interested in giving a talk at an event. イベントでプレゼンテーションをすることに興味があります。</label>
+			</div>
+
+			<div class="question">
+				<p class="required">What is your professional background?&NewLine;履歴・業種を教えてください。</p>
+				{% for id, name in background.items() %}
+					<div class="row">
+						<input id="{{ id }}" type="checkbox" />
+						<label for="{{ id }}">{{ name }}</label>
+					</div>
+				{% endfor %}
+			</div>
+
 			<div class="question">
 				<p class="required">What language would you prefer?&NewLine;どちらの言語がご希望ですか？</p>
 				<select id="language">