feat: SAP icons in editor or hover

[uxkjaer]

Todo:

• Settings for showing icons in editor or only on hover
• Setting to disable icon hover or editor
• On hover functionality
• Code completion for icons
• Update readme with Icons functionality and prerequisite of SAP-icons fonts installed on machine
• Make tests pass
• Add integration tests

fixes #509

[lgtm-com]

This pull request introduces 5 alerts when merging f4effa8 into 352164f - view on LGTM.com

new alerts:

• 5 for Unused variable, import, function or class

[uxkjaer]

Should the sap-icon font-family be added to the editor in the extension or should the user set it themselves in the settings?
@petermuessig @bd82

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[cla-assistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}