Branch add grp

[neoruien]

1. Add Excel XLSX file support
2. Change implementation of the code such that XLSX files will be handled instead of CSV files
3. Fix addgrp bug (Close addgrp allowing multiple groups with same name #113)

[codecov-io]

Codecov Report

Merging #125 into master will decrease coverage by 11.87%.
The diff coverage is 26.95%.

@@              Coverage Diff              @@
##             master     #125       +/-   ##
=============================================
- Coverage     47.61%   35.73%   -11.88%     
+ Complexity      597      376      -221     
=============================================
  Files           146      118       -28     
  Lines          2745     2233      -512     
  Branches        328      271       -57     
=============================================
- Hits           1307      798      -509     
- Misses         1360     1361        +1     
+ Partials         78       74        -4     

Impacted Files	Coverage Δ	Complexity Δ
src/main/java/team/serenity/Main.java	0.00% <ø> (ø)	0.00 <0.00> (?)
src/main/java/team/serenity/MainApp.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...in/java/team/serenity/commons/core/LogsCenter.java	78.37% <ø> (ø)	10.00 <0.00> (?)
...main/java/team/serenity/commons/core/Messages.java	0.00% <ø> (ø)	0.00 <0.00> (?)
...ty/commons/exceptions/DataConversionException.java	100.00% <ø> (ø)	1.00 <0.00> (?)
...nity/commons/exceptions/IllegalValueException.java	50.00% <ø> (ø)	1.00 <0.00> (?)
.../main/java/team/serenity/commons/util/AppUtil.java	88.88% <ø> (ø)	5.00 <0.00> (?)
...ava/team/serenity/commons/util/CollectionUtil.java	87.50% <ø> (ø)	5.00 <0.00> (?)
...in/java/team/serenity/commons/util/ConfigUtil.java	75.00% <ø> (ø)	2.00 <0.00> (?)
.../main/java/team/serenity/commons/util/CsvUtil.java	12.24% <0.00%> (ø)	3.00 <0.00> (?)
... and 131 more

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