Fix bugs regarding index of viewed object

[hanscau]

Index of viewed object was dependent on filteredList to be updated which depended on viewedObject to be updated first. It is possible to update indexOfViewedObject together with viewedObject without waiting for filteredList to be updated. So it is refactored out

[codecov]

Codecov Report

Attention: Patch coverage is 92.68030% with 68 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/main/java/seedu/eventtory/MainApp.java	0.00%	13 Missing ⚠️
.../main/java/seedu/eventtory/model/ModelManager.java	95.51%	0 Missing and 7 partials ⚠️
...ttory/model/association/UniqueAssociationList.java	83.33%	4 Missing and 2 partials ⚠️
...enttory/logic/commands/util/IndexResolverUtil.java	87.50%	0 Missing and 4 partials ⚠️
...u/eventtory/storage/JsonSerializableEventTory.java	91.30%	1 Missing and 3 partials ⚠️
...eedu/eventtory/logic/parser/EditCommandParser.java	93.87%	0 Missing and 3 partials ⚠️
...ava/seedu/eventtory/model/util/SampleDataUtil.java	0.00%	3 Missing ⚠️
.../seedu/eventtory/storage/JsonEventToryStorage.java	85.71%	3 Missing ⚠️
.../main/java/seedu/eventtory/logic/LogicManager.java	84.61%	2 Missing ⚠️
...edu/eventtory/logic/commands/EditEventCommand.java	96.72%	0 Missing and 2 partials ⚠️
... and 13 more

Files with missing lines	Coverage Δ	Complexity Δ
src/main/java/seedu/eventtory/AppParameters.java	95.65% <ø> (ø)	12.00 <0.00> (?)
src/main/java/seedu/eventtory/Main.java	0.00% <ø> (ø)	0.00 <0.00> (?)
...main/java/seedu/eventtory/commons/core/Config.java	77.27% <ø> (ø)	9.00 <0.00> (?)
...java/seedu/eventtory/commons/core/GuiSettings.java	76.92% <ø> (ø)	8.00 <0.00> (?)
.../java/seedu/eventtory/commons/core/LogsCenter.java	78.78% <ø> (ø)	5.00 <0.00> (?)
...ain/java/seedu/eventtory/commons/core/Version.java	82.50% <ø> (ø)	19.00 <0.00> (?)
...java/seedu/eventtory/commons/core/index/Index.java	100.00% <ø> (ø)	11.00 <0.00> (?)
...ttory/commons/exceptions/DataLoadingException.java	100.00% <ø> (ø)	1.00 <0.00> (?)
...tory/commons/exceptions/IllegalValueException.java	100.00% <ø> (ø)	2.00 <0.00> (?)
...ain/java/seedu/eventtory/commons/util/AppUtil.java	88.88% <ø> (ø)	5.00 <0.00> (?)
... and 89 more

... and 7 files with indirect coverage changes