Rename "backend" to "service" in UI (#55), rephrase list description

For most people, "service" is more understandable than "backend". Also changed the wording of the introductory sentence in the DiscoverSection because this is not necessarily the list of *all* backends, just the ones we know of.

src/components/AboutSection.vue

@@ -1,7 +1,7 @@
 <template>
     <section id="about">
-		<p><strong>openEO hub</strong> is a tool to discover backends that support the openEO API. It is also an exchange platform to share process graphs among the openEO community.</p>
-		<p>The data is crawled from the backends and then cached, so may lag behind reality.</p>
+		<p><strong>openEO hub</strong> is a tool to discover services that support the openEO API. It is also an exchange platform to share process graphs among the openEO community.</p>
+		<p>The data is crawled from the services and then cached, so may lag behind reality.</p>
 		<p>For more information on openEO, visit the project's homepage: <a href="https://openeo.org/">https://openeo.org/</a></p>
 		<p>The source code of this website is available <a href="https://github.com/Open-EO/openeo-hub">on GitHub</a>.</p>
 	</section>

src/components/Backend.vue

@@ -28,8 +28,8 @@
 
         <UnsuccessfulCrawlNotice :unsuccessfulCrawls="backend.unsuccessfulCrawls"></UnsuccessfulCrawlNotice>
         <DataRetrievedNotice :timestamp="backend.retrieved"></DataRetrievedNotice>
-        <div v-if="preparedBackend.api_version > '1' && !preparedBackend.production" class="warning">⚠ This backend is NOT production-ready.</div>
-        <div v-if="preparedBackend.api_version > '1' &&  preparedBackend.production" class="info">✔️ This backend is production-ready.</div>
+        <div v-if="preparedBackend.api_version > '1' && !preparedBackend.production" class="warning">⚠ This service is NOT production-ready.</div>
+        <div v-if="preparedBackend.api_version > '1' &&  preparedBackend.production" class="info">✔️ This service is production-ready.</div>
 
         <dl>
             <dt v-if="backend.endpoints" @click="collapsed.functionalities = !collapsed.functionalities">

src/components/DiscoverSection.vue

@@ -1,7 +1,7 @@
 <template>
     <section id="discover">
 		<section id="discover-list">
-			<p>This is a list of all available openEO backends:</p>
+			<p>This is a list of all known openEO providers and their services:</p>
 			<ul class="backendlist">
 				<li v-for="group in allBackendGroups" :key="group.name" v-show="checkFilters(group.backends)" >
 					<BackendGroup :groupName="group.name" :backends="group.backends"></BackendGroup>

src/components/UnsuccessfulCrawlNotice.vue

@@ -1,6 +1,6 @@
 <template>
     <div v-if="needsFlag()" class="unsuccessfulCrawlNotice">
-        ⚠ This backend was recently unavailable for crawling.
+        ⚠ This service was recently unavailable for crawling.
     </div>
 </template>