Edit Time class to allow more time input formats

[solkim-83]

Previously, only the following format for event time was allowed as an user input:

1. dd-MM-yyyy HH:mm

I've changed the Time class to accept more formats such as:

1. dd-MM-yyyy HH:mm
2. yyyy-MM-dd HH:mm
3. and such that [.][/][-] can be used interchangeably to key in the date and time.

[codecov-io]

Codecov Report

Merging #237 into master will increase coverage by 0.76%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #237      +/-   ##
============================================
+ Coverage     60.60%   61.37%   +0.76%     
- Complexity      886      923      +37     
============================================
  Files           140      140              
  Lines          3315     3350      +35     
  Branches        391      396       +5     
============================================
+ Hits           2009     2056      +47     
+ Misses         1128     1117      -11     
+ Partials        178      177       -1     

Impacted Files	Coverage Δ	Complexity Δ
...address/logic/commands/events/AddEventCommand.java	55.22% <ø> (ø)	10.00 <0.00> (ø)
src/main/java/seedu/address/model/event/Time.java	63.82% <100.00%> (ø)	15.00 <1.00> (ø)
.../logic/parser/events/DeleteEventCommandParser.java	50.00% <0.00%> (-7.15%)	2.00% <0.00%> (ø%)
...ddress/logic/commands/events/EditEventCommand.java	71.96% <0.00%> (-0.26%)	16.00% <0.00%> (ø%)
src/main/java/seedu/address/model/tag/TagTree.java	100.00% <0.00%> (ø)	7.00% <0.00%> (ø%)
...java/seedu/address/logic/commands/CommandType.java	100.00% <0.00%> (ø)	7.00% <0.00%> (+2.00%)
...java/seedu/address/logic/commands/CommandWord.java	100.00% <0.00%> (ø)	9.00% <0.00%> (+4.00%)
...ic/parser/contacts/DeleteContactCommandParser.java	100.00% <0.00%> (ø)	2.00% <0.00%> (ø%)
...main/java/seedu/address/model/tag/TagTreeImpl.java	87.64% <0.00%> (+0.14%)	44.00% <0.00%> (+2.00%)
...in/java/seedu/address/logic/parser/ParserUtil.java	89.61% <0.00%> (+0.27%)	26.00% <0.00%> (ø%)
... and 3 more

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[fyshhh]

i think this is inconsistent with the actual pattern below.

[LinkedInk]

lgtm