[ticket/13023] Add template event posting_editor_buttons_custom_tags_before


[PHPBB3-13023](https://tracker.phpbb.com/browse/PHPBB3-13023)
I don't see a more "correct" solution here since it's all a mess. `posting_editor_buttons_after`, for one, really should not be where it is in subsilver2 since it is not in fact after all of the buttons. It should probably be before `<!-- IF S_BBCODE_ALLOWED -->`... which then entails making the event's content its own &lt;tr&gt;, whereas its corresponding `before` event would be inline. My suggestion would be to get rid of the custom bbcode &lt;tr&gt; and have div.core-bbcode-buttons and div.custom-bbcode-buttons under the same tr. A snippet of what that would look like:

			<span class="genmed nowrap">{L_FONT_SIZE}{L_COLON} <select class="gensmall bbcode-size" name="addbbcode20" onchange="bbfontstyle('[size=' + this.form.addbbcode20.options[this.form.addbbcode20.selectedIndex].value + ']', '[/size]');this.form.addbbcode20.selectedIndex = 2;" onmouseover="helpline('f')" onmouseout="helpline('tip')">
				<option value="50">{L_FONT_TINY}</option>
				<option value="85">{L_FONT_SMALL}</option>
				<option value="100" selected="selected">{L_FONT_NORMAL}</option>
				<!-- IF not MAX_FONT_SIZE or MAX_FONT_SIZE >= 150 -->
					<option value="150">{L_FONT_LARGE}</option>
					<!-- IF not MAX_FONT_SIZE or MAX_FONT_SIZE >= 200 -->
						<option value="200">{L_FONT_HUGE}</option>
					<!-- ENDIF -->
				<!-- ENDIF -->
			</select></span>
		</div>
		<!-- EVENT posting_editor_buttons_custom_tags_before -->
		<!-- IF .custom_tags -->
			<div id="custom-bbcode-buttons">
			<!-- BEGIN custom_tags -->
				<input type="button" class="btnbbcode bbcode-{custom_tags.BBCODE_TAG_CLEAN}" name="addbbcode{custom_tags.BBCODE_ID}" value="{custom_tags.BBCODE_TAG}" onclick="bbstyle({custom_tags.BBCODE_ID})"<!-- IF custom_tags.BBCODE_HELPLINE !== '' --> onmouseover="helpline('cb_{custom_tags.BBCODE_ID}')" onmouseout="helpline('tip')"<!-- ENDIF --> />
			<!-- END custom_tags -->
			</div>
		<!-- ENDIF -->
		<!-- EVENT posting_editor_buttons_after -->
	<!-- ENDIF -->
		</td>
	</tr>
	<!-- IF S_BBCODE_ALLOWED -->