Change Icon type to String and add Application type field to in AppSchema

[medchedli]

Replaced the application Icon type from Buffer to String and added application type (which can holds either "link" or "embedded" as values)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (69e71eb) 86.75% compared to head (c021fcb) 86.76%.

:exclamation: Current head c021fcb differs from pull request most recent head 47e908d. Consider uploading reports for the commit 47e908d to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1211 +/- ## ========================================== + Coverage 86.75% 86.76% +0.01% ========================================== Files 89 89 Lines 6024 6024 ========================================== + Hits 5226 5227 +1 + Misses 798 797 -1 ``` | [Files](https://app.codecov.io/gh/jembi/openhim-core-js/pull/1211?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=jembi) | Coverage Δ | | |---|---|---| | [src/model/apps.js](https://app.codecov.io/gh/jembi/openhim-core-js/pull/1211?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=jembi#diff-c3JjL21vZGVsL2FwcHMuanM=) | `100.00% <100.00%> (ø)` | | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/jembi/openhim-core-js/pull/1211/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=jembi)

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[medchedli]

Duplicate of #1212