Update Presets file format

[stoecker]

Reworking of presets file form as discussed in merkaartor mailinglist under the topic "Templatized tagging committed".

a)
Change

       <label text="Edit a Motorway" />
       <label text=" " />
       ...
       <label text="Optional Attributes:" />
       <label text=" " />
       ...

into

  <description text="Edit a Motorway" />
  ...
  <optional>
    ...
  </optional>

b) Allow conditions and change combo boxes:

   <item name="Muslim mosque" condition="[religion] is muslim">

   <item name="Place of worship">
      <choice key="religion">
        <element value="christian">
        <element value="muslim">
      </choice>
      <choice key="denomination">
        <element condition="[religion] is muslim" value="shia">
        <element condition="[religion] is christian" value="protestant">
      </choice>
   </item>

c) Allow include:

i.e. <define name="xxx" mode="set">...</define>
and later use <define name="xxx" mode="get"/>
(or something alike) to prevent repeating information.

d) add a <link> tag to supply link's to the MapFeatures page.

[anonymous]

d) is resolved with r1319

[anonymous]

a) <optional> of a is included as well.

[anonymous]

See also #1552.