BUG: remove FixValue, fix linting errors, move and complete get_status_description

Summary

Client-side fix (or rather clean-up) of caosdb-server#169 (closed).

This MR removes the FixValue work-around (which is needed until caosdb-server!27 (merged)) and adds the missing grpc::StatusCode mappings to caosdb::StatusCode (unrelated to caosdb-server!27 (merged), but it was convenient for debugging to do this now).

Additionally, it fixes some linter warnings in ccaosdb.

Focus

• Implementation of get_status_description moved from "transaction.cpp" to "status_code_description.cpp".
• FixValue and FixValueImpl have been removed.
• Nothing needed to be done here for the fix of the unit problems (#10 (closed))

Test Environment

• Integration tests in caosdb-cppinttest!13 (merged) for both #10 (closed) and caosdb-server#169 (closed)
• No manual testing needed I'd say

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mentioned in issue #10 (closed)

changed the description

added 2 commits

• acdd1f0f - 1 commit from branch dev
• 22e7156f - Merge branch 'dev' into f-value-and-unit

Compare with previous version

added 1 commit

• 526cfca2 - REL: version bump to 0.0.14

Compare with previous version

mentioned in issue caosdb-server#169 (closed)

changed the description

marked the checklist item Up-to-date CHANGELOG.md as completed

marked the checklist item Reference related Issues as completed

marked the checklist item Annotations in code (Gitlab comments) as completed

marked the checklist item All automated tests pass as completed

requested review from @daniel

resolved all threads

marked the checklist item I understand the intent of this MR as completed