Add automation for new PRs and issues

.github/labeler.yml

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+# Add 'in:altcoins' and 'is:no-priority' to any file changes within 'assets' folder
+in:altcoins: assets/*
+is:no-priority: assets/*

.github/workflows/greetings.yml

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+name: Greetings
+
+on: [pull_request, issues]
+
+jobs:
+    greeting:
+        runs-on: ubuntu-latest
+        steps:
+            -   uses: actions/first-interaction@v1
+                with:
+                    repo-token: ${{ secrets.GITHUB_TOKEN }}
+                    issue-message: "**Thanks for opening your first issue here!**<br/><br/>Be sure to follow the issue template. Your issue will be reviewed by a maintainer and labeled for further action."
+                    pr-message: "**Thanks for opening this pull request!**<br/><br/>Please check out our [contributor checklist](https://docs.bisq.network/contributor-checklist.html) and check if *Travis* or *Codacy* found any issues with your PR. Also make sure your commits are signed, and that you applied [Bisq's code style](https://github.com/bisq-network/style/issues) and [formatting](.editorconfig).<br/><br/>A maintainer will add an `is:priority` label to your PR if it is up for compensation. Please see our [Bisq Q1 2020 Update](https://youtu.be/oImSdIAsywA) for more details."

.github/workflows/label.yml

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+name: Pull Request Labeler
+on: [pull_request]
+
+jobs:
+    label:
+
+        runs-on: ubuntu-latest
+
+        steps:
+            -   uses: actions/labeler@v2
+                with:
+                    repo-token: "${{ secrets.GITHUB_TOKEN }}"