Fix broken Return key in export route dialog

2a431932 made it possible to press `Return` to confirm the export dialog.
After 5b52abc1 this stopped working though, even when the text input had focus.

This is due to moving the `<input>` out of the `<form>` and referencing the
form's `name` attribute instead. However "The value of [the form] attribute
must be the id of a <form> in the same document" according to
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/button.

Adding such an `id` restores the `Return` key to working properly.

The same change is done for the no-go form, where the same issue would otherwise
affect a later patch adding similar `Return` key handling.

Test Plan:
- Create Route, open "Export route" dialog.
- Move focus to an input field.
- Press `Return`.
- The file dialog for saving should open.

index.html

@@ -427,7 +427,7 @@
                         </button>
                     </div>
                     <div class="modal-body">
-                        <form name="export">
+                        <form name="export" id="exportForm">
                             <div class="form-group row">
                                 <label class="col-form-label col-sm-2" data-i18n="export.trackname">Name</label>
                                 <div class="col-sm-10">
@@ -519,7 +519,7 @@
                             type="submit"
                             class="btn btn-primary"
                             data-i18n="export.title"
-                            form="export"
+                            form="exportForm"
                             id="submitExport"
                         >
                             Export route
@@ -712,7 +712,7 @@
                     </div>
                     <div class="modal-body">
                         <p id="nogoError" class="invalid-feedback" style="display: none"></p>
-                        <form name="loadNogosForm">
+                        <form name="loadNogosForm" id="loadNogosForm">
                             <fieldset>
                                 <legend data-i18n="loadNogos.source">Source</legend>
                                 <div>